diff --git a/Code/GraphMol/Atom.cpp b/Code/GraphMol/Atom.cpp
index be5b8fd4b..1ef4d098a 100644
--- a/Code/GraphMol/Atom.cpp
+++ b/Code/GraphMol/Atom.cpp
@@ -277,7 +277,7 @@ int Atom::calcExplicitValence(bool strict) {
              << effectiveValence << ", is greater than permitted";
       std::string msg = errout.str();
       BOOST_LOG(rdErrorLog) << msg << std::endl;
-      throw MolSanitizeException(msg);
+      throw AtomValenceException(msg, getIdx());
     }
   }
   d_explicitValence = res;
@@ -391,7 +391,7 @@ int Atom::calcImplicitValence(bool strict) {
                << " not equal to any accepted valence\n";
         std::string msg = errout.str();
         BOOST_LOG(rdErrorLog) << msg << std::endl;
-        throw MolSanitizeException(msg);
+        throw AtomValenceException(msg, getIdx());
       }
       res = 0;
     }
@@ -416,7 +416,7 @@ int Atom::calcImplicitValence(bool strict) {
                << " greater than permitted";
         std::string msg = errout.str();
         BOOST_LOG(rdErrorLog) << msg << std::endl;
-        throw MolSanitizeException(msg);
+        throw AtomValenceException(msg, getIdx());
       } else {
         res = 0;
       }
diff --git a/Code/GraphMol/Kekulize.cpp b/Code/GraphMol/Kekulize.cpp
index e0dc004f4..41aae9c8c 100644
--- a/Code/GraphMol/Kekulize.cpp
+++ b/Code/GraphMol/Kekulize.cpp
@@ -103,7 +103,7 @@ void markDbondCands(RWMol &mol, const INT_VECT &allAtms,
           errout << "Aromatic bonds on non aromatic atom " << at->getIdx();
           std::string msg = errout.str();
           BOOST_LOG(rdErrorLog) << msg << std::endl;
-          throw MolSanitizeException(msg);
+          throw AtomKekulizeException(msg, at->getIdx());
         }
         ++beg;
       }
@@ -466,16 +466,20 @@ void kekulizeFused(RWMol &mol, const VECT_INT_VECT &arings,
     // we exhausted all option (or crossed the allowed
     // number of backTracks) and we still need to backtrack
     // can't kekulize this thing
+    std::vector<unsigned int> problemAtoms;
     std::ostringstream errout;
     errout << "Can't kekulize mol.";
     errout << "  Unkekulized atoms:";
     for (unsigned int i = 0; i < nats; ++i) {
-      if (dBndCands[i]) errout << " " << i;
+      if (dBndCands[i]) {
+        errout << " " << i;
+        problemAtoms.push_back(i);
+      }
     }
     errout << std::endl;
     std::string msg = errout.str();
     BOOST_LOG(rdErrorLog) << msg << std::endl;
-    throw MolSanitizeException(msg);
+    throw KekulizeException(msg, problemAtoms);
   }
 }
 }  // namespace
@@ -592,7 +596,7 @@ void Kekulize(RWMol &mol, bool markAtomsBonds, unsigned int maxBackTracks) {
           errout << "non-ring atom " << (*ai)->getIdx() << " marked aromatic";
           std::string msg = errout.str();
           BOOST_LOG(rdErrorLog) << msg << std::endl;
-          throw MolSanitizeException(msg);
+          throw AtomKekulizeException(msg, (*ai)->getIdx());
         }
         (*ai)->setIsAromatic(false);
         // make sure "explicit" Hs on things like pyrroles don't hang around
@@ -619,7 +623,7 @@ void Kekulize(RWMol &mol, bool markAtomsBonds, unsigned int maxBackTracks) {
              << ": " << val << "!=" << valences[i] << std::endl;
       std::string msg = errout.str();
       BOOST_LOG(rdErrorLog) << msg << std::endl;
-      throw MolSanitizeException(msg);
+      throw AtomKekulizeException(msg, (*ai)->getIdx());
     }
     i++;
   }
diff --git a/Code/GraphMol/MolOps.cpp b/Code/GraphMol/MolOps.cpp
index a12360b4d..ea959c20e 100644
--- a/Code/GraphMol/MolOps.cpp
+++ b/Code/GraphMol/MolOps.cpp
@@ -383,6 +383,48 @@ void sanitizeMol(RWMol &mol, unsigned int &operationThatFailed,
   operationThatFailed = 0;
 }
 
+std::vector<std::unique_ptr<MolSanitizeException>> detectChemistryProblems(
+    const ROMol &imol, unsigned int sanitizeOps) {
+  RWMol mol(imol);
+  std::vector<std::unique_ptr<MolSanitizeException>> res;
+
+  // clear out any cached properties
+  mol.clearComputedProps();
+
+  int operation;
+  operation = SANITIZE_CLEANUP;
+  if (sanitizeOps & operation) {
+    // clean up things like nitro groups
+    cleanUp(mol);
+  }
+
+  // update computed properties on atoms and bonds:
+  operation = SANITIZE_PROPERTIES;
+  if (sanitizeOps & operation) {
+    for (auto &atom : mol.atoms()) {
+      try {
+        bool strict = true;
+        atom->updatePropertyCache(strict);
+      } catch (const MolSanitizeException &e) {
+        res.emplace_back(e.copy());
+      }
+    }
+  } else {
+    mol.updatePropertyCache(false);
+  }
+
+  // kekulizations
+  operation = SANITIZE_KEKULIZE;
+  if (sanitizeOps & operation) {
+    try {
+      Kekulize(mol);
+    } catch (const MolSanitizeException &e) {
+      res.emplace_back(e.copy());
+    }
+  }
+  return res;
+}
+
 std::vector<ROMOL_SPTR> getMolFrags(const ROMol &mol, bool sanitizeFrags,
                                     INT_VECT *frags,
                                     VECT_INT_VECT *fragsMolAtomMapping,
diff --git a/Code/GraphMol/MolOps.h b/Code/GraphMol/MolOps.h
index 9dd114ae8..4bfaefd6e 100644
--- a/Code/GraphMol/MolOps.h
+++ b/Code/GraphMol/MolOps.h
@@ -20,6 +20,7 @@
 #include <boost/dynamic_bitset.hpp>
 #include <RDGeneral/BoostEndInclude.h>
 #include <RDGeneral/types.h>
+#include "SanitException.h"
 
 RDKIT_GRAPHMOL_EXPORT extern const int ci_LOCAL_INF;
 namespace RDKit {
@@ -378,24 +379,21 @@ typedef enum {
    \param mol : the RWMol to be cleaned
 
    \param operationThatFailed : the first (if any) sanitization operation that
-   fails is set here.
+                                fails is set here.
                                 The values are taken from the \c SanitizeFlags
-   enum.
-                                On success, the value is  \c
-   SanitizeFlags::SANITIZE_NONE
+                                enum. On success, the value is \c
+                                SanitizeFlags::SANITIZE_NONE
 
    \param sanitizeOps : the bits here are used to set which sanitization
-   operations are carried
-                        out. The elements of the \c SanitizeFlags enum define
-   the operations.
+                        operations are carried out. The elements of the \c
+                        SanitizeFlags enum define the operations.
 
    <b>Notes:</b>
-    - If there is a failure in the sanitization, a \c SanitException
+    - If there is a failure in the sanitization, a \c MolSanitizeException
       will be thrown.
     - in general the user of this function should cast the molecule following
-   this
-      function to a ROMol, so that new atoms and bonds cannot be added to the
-      molecule and screw up the sanitizing that has been done here
+      this function to a ROMol, so that new atoms and bonds cannot be added to
+      the molecule and screw up the sanitizing that has been done here
 */
 RDKIT_GRAPHMOL_EXPORT void sanitizeMol(RWMol &mol,
                                        unsigned int &operationThatFailed,
@@ -403,6 +401,32 @@ RDKIT_GRAPHMOL_EXPORT void sanitizeMol(RWMol &mol,
 //! \overload
 RDKIT_GRAPHMOL_EXPORT void sanitizeMol(RWMol &mol);
 
+//! \brief Identifies chemistry problems (things that don't make chemical sense)
+//! in a molecule
+/*!
+   This functions uses the operations in sanitizeMol but does not change
+   the input structure and returns a list of the problems encountered instead of
+   stopping at the first failure,
+
+   The problems this looks for come from the sanitization operations:
+     -# mol.updatePropertyCache()  : Unreasonable valences
+     -# MolOps::Kekulize()  : Unkekulizable ring systems, aromatic atoms not in
+                              rings, aromatic bonds to non-aromatic atoms.
+
+   \param mol : the RWMol to be cleaned
+
+   \param sanitizeOps : the bits here are used to set which sanitization
+                        operations are carried out. The elements of the \c
+                        SanitizeFlags enum define the operations.
+
+   \return a vector of \c MolSanitizeException values that indicate what
+           problems were encountered
+
+*/
+RDKIT_GRAPHMOL_EXPORT
+std::vector<std::unique_ptr<MolSanitizeException>> detectChemistryProblems(
+    const ROMol &mol, unsigned int sanitizeOps = SANITIZE_ALL);
+
 //! Possible aromaticity models
 /*!
 - \c AROMATICITY_DEFAULT at the moment always uses \c AROMATICITY_RDKIT
diff --git a/Code/GraphMol/SanitException.h b/Code/GraphMol/SanitException.h
index d53c719d4..c686cd49e 100644
--- a/Code/GraphMol/SanitException.h
+++ b/Code/GraphMol/SanitException.h
@@ -1,5 +1,5 @@
 //
-//  Copyright (C) 2002-2006 Rational Discovery LLC
+//  Copyright (C) 2002-2019 Greg Landrum and Rational Discovery LLC
 //
 //   @@ All Rights Reserved @@
 //  This file is part of the RDKit.
@@ -9,8 +9,8 @@
 //
 
 #include <RDGeneral/export.h>
-#ifndef _RD_SANITEXCEPTION_H
-#define _RD_SANITEXCEPTION_H
+#ifndef RD_SANITEXCEPTION_H
+#define RD_SANITEXCEPTION_H
 
 #include <RDGeneral/types.h>
 #include <GraphMol/GraphMol.h>
@@ -26,14 +26,93 @@ namespace RDKit {
 //! class for flagging sanitization errors
 class RDKIT_GRAPHMOL_EXPORT MolSanitizeException : public std::exception {
  public:
-  MolSanitizeException(const char *msg) : _msg(msg){};
-  MolSanitizeException(const std::string &msg) : _msg(msg){};
-  const char *message() const { return _msg.c_str(); };
-  ~MolSanitizeException() throw(){};
+  MolSanitizeException(const char *msg) : d_msg(msg){};
+  MolSanitizeException(const std::string &msg) : d_msg(msg){};
+  MolSanitizeException(const MolSanitizeException &other)
+      : d_msg(other.d_msg){};
+  virtual const char *message() const { return d_msg.c_str(); };
+  virtual ~MolSanitizeException() throw(){};
+  virtual MolSanitizeException *copy() const {
+    return new MolSanitizeException(*this);
+  };
+  virtual std::string getType() const { return "MolSanitizeException"; };
 
- private:
-  std::string _msg;
+ protected:
+  std::string d_msg;
 };
+
+class RDKIT_GRAPHMOL_EXPORT AtomSanitizeException
+    : public MolSanitizeException {
+ public:
+  AtomSanitizeException(const char *msg, unsigned int atomIdx)
+      : MolSanitizeException(msg), d_atomIdx(atomIdx){};
+  AtomSanitizeException(const std::string &msg, unsigned int atomIdx)
+      : MolSanitizeException(msg), d_atomIdx(atomIdx){};
+  AtomSanitizeException(const AtomSanitizeException &other)
+      : MolSanitizeException(other), d_atomIdx(other.d_atomIdx){};
+  unsigned int getAtomIdx() const { return d_atomIdx; };
+  virtual ~AtomSanitizeException() throw(){};
+  virtual MolSanitizeException *copy() const {
+    return new AtomSanitizeException(*this);
+  };
+  virtual std::string getType() const { return "AtomSanitizeException"; };
+
+ protected:
+  unsigned int d_atomIdx;
+};
+
+class RDKIT_GRAPHMOL_EXPORT AtomValenceException
+    : public AtomSanitizeException {
+ public:
+  AtomValenceException(const char *msg, unsigned int atomIdx)
+      : AtomSanitizeException(msg, atomIdx){};
+  AtomValenceException(const std::string &msg, unsigned int atomIdx)
+      : AtomSanitizeException(msg, atomIdx){};
+  AtomValenceException(const AtomValenceException &other)
+      : AtomSanitizeException(other){};
+  virtual ~AtomValenceException() throw(){};
+  MolSanitizeException *copy() const {
+    return new AtomValenceException(*this);
+  };
+  std::string getType() const { return "AtomValenceException"; };
+};
+
+class RDKIT_GRAPHMOL_EXPORT AtomKekulizeException
+    : public AtomSanitizeException {
+ public:
+  AtomKekulizeException(const char *msg, unsigned int atomIdx)
+      : AtomSanitizeException(msg, atomIdx){};
+  AtomKekulizeException(const std::string &msg, unsigned int atomIdx)
+      : AtomSanitizeException(msg, atomIdx){};
+  AtomKekulizeException(const AtomKekulizeException &other)
+      : AtomSanitizeException(other){};
+  virtual ~AtomKekulizeException() throw(){};
+  MolSanitizeException *copy() const {
+    return new AtomKekulizeException(*this);
+  };
+  std::string getType() const { return "AtomKekulizeException"; };
+};
+
+class RDKIT_GRAPHMOL_EXPORT KekulizeException : public MolSanitizeException {
+ public:
+  KekulizeException(const char *msg, const std::vector<unsigned int> &indices)
+      : MolSanitizeException(msg), d_atomIndices(indices){};
+  KekulizeException(const std::string &msg,
+                    const std::vector<unsigned int> &indices)
+      : MolSanitizeException(msg), d_atomIndices(indices){};
+  KekulizeException(const KekulizeException &other)
+      : MolSanitizeException(other), d_atomIndices(other.d_atomIndices){};
+  const std::vector<unsigned int> &getAtomIndices() const {
+    return d_atomIndices;
+  };
+  virtual ~KekulizeException() throw(){};
+  MolSanitizeException *copy() const { return new KekulizeException(*this); };
+  std::string getType() const { return "KekulizeException"; };
+
+ protected:
+  std::vector<unsigned int> d_atomIndices;
+};
+
 }  // namespace RDKit
 
 #endif
diff --git a/Code/GraphMol/Wrap/MolOps.cpp b/Code/GraphMol/Wrap/MolOps.cpp
index a66935904..f49e697f5 100644
--- a/Code/GraphMol/Wrap/MolOps.cpp
+++ b/Code/GraphMol/Wrap/MolOps.cpp
@@ -351,6 +351,7 @@ void addRecursiveQuery(ROMol &mol, const ROMol &query, unsigned int atomIdx,
     oAt->expandQuery(q, Queries::COMPOSITE_AND);
   }
 }
+
 MolOps::SanitizeFlags sanitizeMol(ROMol &mol, boost::uint64_t sanitizeOps,
                                   bool catchErrors) {
   RWMol &wmol = static_cast<RWMol &>(mol);
@@ -766,6 +767,16 @@ ROMol *adjustQueryPropertiesHelper(const ROMol &mol, python::object pyparams) {
   return MolOps::adjustQueryProperties(mol, &params);
 }
 
+python::tuple detectChemistryProblemsHelper(const ROMol &mol,
+                                            unsigned int sanitizeOps) {
+  auto probs = MolOps::detectChemistryProblems(mol, sanitizeOps);
+  python::list res;
+  for (const auto &exc_ptr : probs) {
+    res.append(boost::shared_ptr<MolSanitizeException>(exc_ptr->copy()));
+  }
+  return python::tuple(res);
+}
+
 ROMol *replaceCoreHelper(const ROMol &mol, const ROMol &core,
                          python::object match, bool replaceDummies,
                          bool labelByIndex, bool requireDummyMatch = false) {
@@ -2258,6 +2269,11 @@ A note on the flags controlling which atoms/bonds are modified: \n\
                 (python::arg("mol"), python::arg("params") = python::object()),
                 docString.c_str(),
                 python::return_value_policy<python::manage_new_object>());
+    docString = "checks for chemistry problems";
+    python::def(
+        "DetectChemistryProblems", detectChemistryProblemsHelper,
+        (python::arg("mol"), python::arg("sanitizeOps") = MolOps::SANITIZE_ALL),
+        docString.c_str());
   };
 };
 }  // namespace RDKit
diff --git a/Code/GraphMol/Wrap/rdchem.cpp b/Code/GraphMol/Wrap/rdchem.cpp
index 021ab8c51..570a7202f 100644
--- a/Code/GraphMol/Wrap/rdchem.cpp
+++ b/Code/GraphMol/Wrap/rdchem.cpp
@@ -37,12 +37,6 @@ void rdExceptionTranslator(RDKit::ConformerException const &x) {
   PyErr_SetString(PyExc_ValueError, "Bad Conformer Id");
 }
 
-void rdSanitExceptionTranslator(RDKit::MolSanitizeException const &x) {
-  std::ostringstream ss;
-  ss << "Sanitization error: " << x.message();
-  PyErr_SetString(PyExc_ValueError, ss.str().c_str());
-}
-
 void wrap_table();
 void wrap_atom();
 void wrap_conformer();
@@ -116,14 +110,111 @@ void WrapLogs() {
   if (rdWarningLog != nullptr) rdWarningLog->SetTee(warning);
 }
 
+python::tuple getAtomIndicesHelper(const KekulizeException &self) {
+  python::list res;
+  for (auto idx : self.getAtomIndices()) {
+    res.append(idx);
+  }
+  return python::tuple(res);
+}
+
+PyObject *molSanitizeExceptionType = nullptr;
+PyObject *atomSanitizeExceptionType = nullptr;
+PyObject *atomValenceExceptionType = nullptr;
+PyObject *atomKekulizeExceptionType = nullptr;
+PyObject *kekulizeExceptionType = nullptr;
+
+// pattern from here:
+// https://stackoverflow.com/questions/11448735/boostpython-export-custom-exception-and-inherit-from-pythons-exception
+template <typename EXC_TYPE>
+void sanitExceptionTranslator(const EXC_TYPE &x, PyObject *pyExcType) {
+  PRECONDITION(pyExcType != nullptr, "global type not initialized");
+  python::object pyExcInstance(python::handle<>(python::borrowed(pyExcType)));
+  pyExcInstance.attr("cause") = x;
+  PyErr_SetString(pyExcType, x.message());
+}
+
+// pattern from here:
+// https://stackoverflow.com/questions/9620268/boost-python-custom-exception-class
+PyObject *createExceptionClass(const char *name,
+                               PyObject *baseTypeObj = PyExc_ValueError) {
+  std::string scopeName =
+      python::extract<std::string>(python::scope().attr("__name__"));
+  std::string qualifiedName0 = scopeName + "." + name;
+  char *qualifiedName1 = const_cast<char *>(qualifiedName0.c_str());
+
+  PyObject *typeObj = PyErr_NewException(qualifiedName1, baseTypeObj, 0);
+  if (!typeObj) python::throw_error_already_set();
+  python::scope().attr(name) = python::handle<>(python::borrowed(typeObj));
+  return typeObj;
+}
+
 BOOST_PYTHON_MODULE(rdchem) {
   python::scope().attr("__doc__") =
       "Module containing the core chemistry functionality of the RDKit";
   RegisterListConverter<RDKit::Atom *>();
   RegisterListConverter<RDKit::Bond *>();
   rdkit_import_array();
+
+  // this is one of those parts where I think I wish that I knew how to do
+  // template meta-programming
+  python::class_<MolSanitizeException>("_cppMolSanitizeException",
+                                       "exception arising from sanitization",
+                                       python::no_init)
+      .def("Message", &MolSanitizeException::message)
+      .def("GetType", &MolSanitizeException::getType);
+  python::register_ptr_to_python<boost::shared_ptr<MolSanitizeException>>();
+  molSanitizeExceptionType = createExceptionClass("MolSanitizeException");
   python::register_exception_translator<RDKit::MolSanitizeException>(
-      &rdSanitExceptionTranslator);
+      [&](const MolSanitizeException &exc) {
+        sanitExceptionTranslator(exc, molSanitizeExceptionType);
+      });
+
+  python::class_<AtomSanitizeException, python::bases<MolSanitizeException>>(
+      "_cppAtomSanitizeException", "exception arising from sanitization",
+      python::no_init)
+      .def("GetAtomIdx", &AtomSanitizeException::getAtomIdx);
+  python::register_ptr_to_python<boost::shared_ptr<AtomSanitizeException>>();
+  atomSanitizeExceptionType =
+      createExceptionClass("AtomSanitizeException", molSanitizeExceptionType);
+  python::register_exception_translator<RDKit::AtomSanitizeException>(
+      [&](const AtomSanitizeException &exc) {
+        sanitExceptionTranslator(exc, atomSanitizeExceptionType);
+      });
+
+  python::class_<AtomValenceException, python::bases<AtomSanitizeException>>(
+      "_cppAtomValenceException", "exception arising from sanitization",
+      python::no_init);
+  python::register_ptr_to_python<boost::shared_ptr<AtomValenceException>>();
+  atomValenceExceptionType =
+      createExceptionClass("AtomValenceException", atomSanitizeExceptionType);
+  python::register_exception_translator<RDKit::AtomValenceException>(
+      [&](const AtomValenceException &exc) {
+        sanitExceptionTranslator(exc, atomValenceExceptionType);
+      });
+
+  python::class_<AtomKekulizeException, python::bases<AtomSanitizeException>>(
+      "_cppAtomKekulizeException", "exception arising from sanitization",
+      python::no_init);
+  python::register_ptr_to_python<boost::shared_ptr<AtomKekulizeException>>();
+  atomKekulizeExceptionType =
+      createExceptionClass("AtomKekulizeException", atomSanitizeExceptionType);
+  python::register_exception_translator<RDKit::AtomKekulizeException>(
+      [&](const AtomKekulizeException &exc) {
+        sanitExceptionTranslator(exc, atomKekulizeExceptionType);
+      });
+
+  python::class_<KekulizeException, python::bases<MolSanitizeException>>(
+      "_cppAtomKekulizeException", "exception arising from sanitization",
+      python::no_init)
+      .def("GetAtomIndices", &getAtomIndicesHelper);
+  python::register_ptr_to_python<boost::shared_ptr<KekulizeException>>();
+  kekulizeExceptionType =
+      createExceptionClass("KekulizeException", molSanitizeExceptionType);
+  python::register_exception_translator<RDKit::KekulizeException>(
+      [&](const KekulizeException &exc) {
+        sanitExceptionTranslator(exc, kekulizeExceptionType);
+      });
 
   python::def("WrapLogs", WrapLogs,
               "Wrap the internal RDKit streams so they go to python's "
diff --git a/Code/GraphMol/Wrap/rough_test.py b/Code/GraphMol/Wrap/rough_test.py
index 9f3580154..a09c08434 100644
--- a/Code/GraphMol/Wrap/rough_test.py
+++ b/Code/GraphMol/Wrap/rough_test.py
@@ -453,7 +453,7 @@ class TestCase(unittest.TestCase):
     smi1 = Chem.MolToSmiles(m)
     smi2 = Chem.MolToSmiles(m2)
     self.assertTrue(smi1 == smi2)
-    
+
   def test16Props(self):
     m = Chem.MolFromSmiles('C1=CN=CC=C1')
     self.assertTrue(not m.HasProp('prop1'))
@@ -2106,7 +2106,7 @@ CAS<~>
     self.assertTrue(ri.IsBondInRingOfSize(2, 4))
 
 
-    if hasattr(Chem,'FindRingFamilies'): 
+    if hasattr(Chem,'FindRingFamilies'):
       ri = m.GetRingInfo()
       self.assertFalse(ri.AreRingFamiliesInitialized())
       Chem.FindRingFamilies(m)
@@ -5020,16 +5020,16 @@ width='200px' height='200px' >
 
   def testAssignStereochemistryFrom3D(self):
     def _stereoTester(mol,expectedCIP,expectedStereo):
-        mol.UpdatePropertyCache()
-        self.assertEqual(mol.GetNumAtoms(),9)
-        self.assertFalse(mol.GetAtomWithIdx(1).HasProp("_CIPCode"))
-        self.assertEqual(mol.GetBondWithIdx(3).GetStereo(),Chem.BondStereo.STEREONONE)
-        for bond in mol.GetBonds():
-            bond.SetBondDir(Chem.BondDir.NONE)
-        Chem.AssignStereochemistryFrom3D(mol)
-        self.assertTrue(mol.GetAtomWithIdx(1).HasProp("_CIPCode"))
-        self.assertEqual(mol.GetAtomWithIdx(1).GetProp("_CIPCode"),expectedCIP)
-        self.assertEqual(mol.GetBondWithIdx(3).GetStereo(),expectedStereo)
+      mol.UpdatePropertyCache()
+      self.assertEqual(mol.GetNumAtoms(),9)
+      self.assertFalse(mol.GetAtomWithIdx(1).HasProp("_CIPCode"))
+      self.assertEqual(mol.GetBondWithIdx(3).GetStereo(),Chem.BondStereo.STEREONONE)
+      for bond in mol.GetBonds():
+        bond.SetBondDir(Chem.BondDir.NONE)
+      Chem.AssignStereochemistryFrom3D(mol)
+      self.assertTrue(mol.GetAtomWithIdx(1).HasProp("_CIPCode"))
+      self.assertEqual(mol.GetAtomWithIdx(1).GetProp("_CIPCode"),expectedCIP)
+      self.assertEqual(mol.GetBondWithIdx(3).GetStereo(),expectedStereo)
 
     fileN = os.path.join(RDConfig.RDBaseDir, 'Code', 'GraphMol', 'test_data',
                        'stereochem.sdf')
@@ -5041,8 +5041,8 @@ width='200px' height='200px' >
     ("S",Chem.BondStereo.STEREOE),
     )
     for i,mol in enumerate(suppl):
-        cip,stereo = expected[i]
-        _stereoTester(mol,cip,stereo)
+      cip,stereo = expected[i]
+      _stereoTester(mol,cip,stereo)
 
   def testGitHub2082(self):
     ctab="""
@@ -5096,9 +5096,9 @@ M  END
   def testGitHub1985(self):
     # simple check, this used to throw an exception
     try:
-       Chem.MolToSmarts(Chem.MolFromSmarts("[C@]"))
+      Chem.MolToSmarts(Chem.MolFromSmarts("[C@]"))
     except:
-       self.fail("[C@] caused an exception when roundtripping smarts")
+      self.fail("[C@] caused an exception when roundtripping smarts")
 
   def testGetEnhancedStereo(self):
 
@@ -5285,7 +5285,7 @@ M  END
     for atom in m.GetAtoms():
       bv.SetBit(atom.GetIdx())
       atom.SetExplicitBitVectProp("prop", bv)
-      
+
     for atom in m.GetAtoms():
       bv = atom.GetExplicitBitVectProp("prop")
       self.assertTrue(bv.GetBit(atom.GetIdx()))
@@ -5302,7 +5302,7 @@ M  END
     for atom in m.GetAtoms():
       if atom.GetIdx() == 0:
         atom.SetExplicitBitVectProp("prop", bv)
-      
+
     l = tuple([x.GetIdx() for x in m.GetAtomsMatchingQuery(qa)])
     self.assertEqual(l, (0,))
 
@@ -5311,37 +5311,37 @@ M  END
       bv = DataStructs.ExplicitBitVect(4)
       bv.SetBit(atom.GetIdx())
       atom.SetExplicitBitVectProp("prop", bv)
-        
+
     sma = Chem.MolFromSmarts("C")
     for atom in sma.GetAtoms():
-        bv = DataStructs.ExplicitBitVect(4)
-        bv.SetBit(1)
-        qa = rdqueries.HasBitVectPropWithValueQueryAtom("prop", bv, tolerance=0.0)
-        atom.ExpandQuery(qa)
+      bv = DataStructs.ExplicitBitVect(4)
+      bv.SetBit(1)
+      qa = rdqueries.HasBitVectPropWithValueQueryAtom("prop", bv, tolerance=0.0)
+      atom.ExpandQuery(qa)
 
     res = m.GetSubstructMatches(sma)
     self.assertEqual(res, ((1,),))
 
     sma = Chem.MolFromSmarts("C")
     for atom in sma.GetAtoms():
-        bv = DataStructs.ExplicitBitVect(4)
-        bv.SetBit(0)
-        qa = rdqueries.HasBitVectPropWithValueQueryAtom("prop", bv, tolerance=0.0)
-        atom.ExpandQuery(qa)
+      bv = DataStructs.ExplicitBitVect(4)
+      bv.SetBit(0)
+      qa = rdqueries.HasBitVectPropWithValueQueryAtom("prop", bv, tolerance=0.0)
+      atom.ExpandQuery(qa)
 
     res = m.GetSubstructMatches(sma)
     self.assertEqual(res, ((0,),))
-    
+
     sma = Chem.MolFromSmarts("C")
     for atom in sma.GetAtoms():
-        bv = DataStructs.ExplicitBitVect(4)
-        bv.SetBit(0)
-        qa = rdqueries.HasBitVectPropWithValueQueryAtom("prop", bv, tolerance=1.0)
-        atom.ExpandQuery(qa)
+      bv = DataStructs.ExplicitBitVect(4)
+      bv.SetBit(0)
+      qa = rdqueries.HasBitVectPropWithValueQueryAtom("prop", bv, tolerance=1.0)
+      atom.ExpandQuery(qa)
 
     res = m.GetSubstructMatches(sma)
     self.assertEqual(res, ((0,),(1,)))
-        
+
   def testGithub2441(self):
     m = Chem.MolFromSmiles("CC")
     conf = Chem.Conformer(2)
@@ -5387,7 +5387,7 @@ C1C(Cl)CCCC duff2
     l = [x for x in suppl2]
     self.assertEqual(len(l),7)
     self.assertTrue(l[6] is None)
-      
+
     sdf=b"""
   Mrv1810 06051911332D          
 
@@ -5422,7 +5422,7 @@ $$$$
     self.assertEqual(len(l),3)
     self.assertTrue(l[1] is None)
     self.assertTrue(l[2] is None)
-    
+
     from io import BytesIO
     sio = BytesIO(sdf)
     suppl3 = Chem.ForwardSDMolSupplier(sio)
@@ -5430,7 +5430,7 @@ $$$$
     self.assertEqual(len(l),3)
     self.assertTrue(l[1] is None)
     self.assertTrue(l[2] is None)
-      
+
     sdf=b"""
   Mrv1810 06051911332D          
 
@@ -5464,7 +5464,7 @@ M  END
     self.assertEqual(len(l),2)
     self.assertTrue(l[0] is not None)
     self.assertTrue(l[1] is not None)
-    
+
     from io import BytesIO
     sio = BytesIO(sdf)
     suppl3 = Chem.ForwardSDMolSupplier(sio)
@@ -5499,6 +5499,48 @@ H      0.635000    0.635000    0.635000
 
     self.assertEqual(Chem.MolToXYZBlock(mol), xyzblock_expected)
 
+  def testSanitizationExceptionBasics(self):
+    try:
+      Chem.SanitizeMol(Chem.MolFromSmiles('CFC',sanitize=False))
+    except Chem.AtomValenceException as exc:
+      self.assertEqual(exc.cause.GetAtomIdx(),1)
+    else:
+      self.assertFalse(True)
+      
+    try:
+      Chem.SanitizeMol(Chem.MolFromSmiles('c1cc1',sanitize=False))
+    except Chem.KekulizeException as exc:
+      self.assertEqual(exc.cause.GetAtomIndices(),(0,1,2))
+    else:
+      self.assertFalse(True)
+          
+
+  def testSanitizationExceptionHierarchy(self):
+    with self.assertRaises(Chem.AtomValenceException):
+      Chem.SanitizeMol(Chem.MolFromSmiles('CFC',sanitize=False))
+    with self.assertRaises(Chem.AtomSanitizeException):
+      Chem.SanitizeMol(Chem.MolFromSmiles('CFC',sanitize=False))
+    with self.assertRaises(Chem.MolSanitizeException):
+      Chem.SanitizeMol(Chem.MolFromSmiles('CFC',sanitize=False))
+    with self.assertRaises(ValueError):
+      Chem.SanitizeMol(Chem.MolFromSmiles('CFC',sanitize=False))
+
+    with self.assertRaises(Chem.KekulizeException):
+      Chem.SanitizeMol(Chem.MolFromSmiles('c1cc1',sanitize=False))
+    with self.assertRaises(Chem.MolSanitizeException):
+      Chem.SanitizeMol(Chem.MolFromSmiles('c1cc1',sanitize=False))
+    with self.assertRaises(ValueError):
+      Chem.SanitizeMol(Chem.MolFromSmiles('c1cc1', sanitize=False))
+
+  def testDetectChemistryProblems(self):
+    m = Chem.MolFromSmiles('CFCc1cc1ClC',sanitize=False)
+    ps = Chem.DetectChemistryProblems(m)
+    self.assertEqual(len(ps),3)
+    self.assertEqual([x.GetType() for x in ps],['AtomValenceException','AtomValenceException','KekulizeException'])
+    self.assertEqual(ps[0].GetAtomIdx(),1)
+    self.assertEqual(ps[1].GetAtomIdx(),6)
+    self.assertEqual(ps[2].GetAtomIndices(),(3,4,5))
+
   def testGithub2611(self):
     mol = Chem.MolFromSmiles('ONCS.ONCS')
     for atom in mol.GetAtoms():
@@ -5526,7 +5568,6 @@ H      0.635000    0.635000    0.635000
           self.assertEqual(order1,order3)
           self.assertEqual(order2,order4)
     
-
 if __name__ == '__main__':
   if "RDTESTCASE" in os.environ:
     suite = unittest.TestSuite()
diff --git a/Code/GraphMol/catch_tests.cpp b/Code/GraphMol/catch_tests.cpp
index b4581a2bc..7f9959ce5 100644
--- a/Code/GraphMol/catch_tests.cpp
+++ b/Code/GraphMol/catch_tests.cpp
@@ -340,6 +340,82 @@ M  END)CTAB";
   }
 }
 
+TEST_CASE("Specialized exceptions for sanitization errors", "[molops]") {
+  SECTION("AtomValenceException") {
+    std::vector<std::pair<std::string, unsigned int>> smiles = {
+        {"C=n1ccnc1", 1}, {"CCO(C)C", 2}};
+    for (auto pr : smiles) {
+      CHECK_THROWS_AS(SmilesToMol(pr.first), AtomValenceException);
+      try {
+        auto m = SmilesToMol(pr.first);
+      } catch (const AtomValenceException &e) {
+        CHECK(e.getType() == "AtomValenceException");
+        CHECK(e.getAtomIdx() == pr.second);
+      }
+    }
+  }
+  SECTION("AtomKekulizeException") {
+    std::vector<std::pair<std::string, unsigned int>> smiles = {
+        {"CCcc", 2}, {"C1:c:CC1", 0}};
+    for (auto pr : smiles) {
+      CHECK_THROWS_AS(SmilesToMol(pr.first), AtomKekulizeException);
+      try {
+        auto m = SmilesToMol(pr.first);
+      } catch (const AtomKekulizeException &e) {
+        CHECK(e.getType() == "AtomKekulizeException");
+        CHECK(e.getAtomIdx() == pr.second);
+      }
+    }
+  }
+  SECTION("KekulizeException") {
+    std::vector<std::pair<std::string, std::vector<unsigned int>>> smiles = {
+        {"c1cccc1", {0, 1, 2, 3, 4}}, {"Cc1cc1", {1, 2, 3}}};
+    for (auto pr : smiles) {
+      CHECK_THROWS_AS(SmilesToMol(pr.first), KekulizeException);
+      try {
+        auto m = SmilesToMol(pr.first);
+      } catch (const KekulizeException &e) {
+        CHECK(e.getType() == "KekulizeException");
+        CHECK(e.getAtomIndices() == pr.second);
+      }
+    }
+  }
+}
+
+TEST_CASE("detectChemistryProblems", "[molops]") {
+  SECTION("Basics") {
+    SmilesParserParams ps;
+    ps.sanitize = false;
+    auto m = std::unique_ptr<ROMol>(SmilesToMol("CO(C)CFCc1cc1", ps));
+    REQUIRE(m);
+    auto res = MolOps::detectChemistryProblems(*m);
+    REQUIRE(res.size() == 3);
+
+    CHECK(res[0]->getType() == "AtomValenceException");
+    REQUIRE(dynamic_cast<AtomValenceException *>(res[0].get()));
+    CHECK(dynamic_cast<AtomSanitizeException *>(res[0].get())->getAtomIdx() ==
+          1);
+
+    CHECK(res[1]->getType() == "AtomValenceException");
+    REQUIRE(dynamic_cast<AtomSanitizeException *>(res[1].get()));
+    CHECK(dynamic_cast<AtomSanitizeException *>(res[1].get())->getAtomIdx() ==
+          4);
+
+    CHECK(res[2]->getType() == "KekulizeException");
+    REQUIRE(dynamic_cast<KekulizeException *>(res[2].get()));
+    CHECK(dynamic_cast<KekulizeException *>(res[2].get())->getAtomIndices() ==
+          std::vector<unsigned int>({6, 7, 8}));
+  }
+  SECTION("No problems") {
+    SmilesParserParams ps;
+    ps.sanitize = false;
+    auto m = std::unique_ptr<ROMol>(SmilesToMol("c1ccccc1", ps));
+    REQUIRE(m);
+    auto res = MolOps::detectChemistryProblems(*m);
+    REQUIRE(res.size() == 0);
+  }
+}
+
 TEST_CASE(
     "github #2606: Bad valence corrections on Pb, Sn"
     "[bug, molops]") {
@@ -433,4 +509,4 @@ M  END
     CHECK(mol->getAtomWithIdx(0)->getFormalCharge() == 2);
     CHECK(mol->getAtomWithIdx(0)->getTotalNumHs() == 0);
   }
-}
\ No newline at end of file
+}
diff --git a/Code/JavaWrappers/MolOps.i b/Code/JavaWrappers/MolOps.i
index 6fed6a9e2..40fefa4df 100644
--- a/Code/JavaWrappers/MolOps.i
+++ b/Code/JavaWrappers/MolOps.i
@@ -1,5 +1,4 @@
 /*
-* $Id$
 *
 *  Copyright (c) 2010, Novartis Institutes for BioMedical Research Inc.
 *  All rights reserved.
@@ -35,10 +34,12 @@
 #include <GraphMol/MolOps.h>
 %}
 
+%template(MolSanitizeException_Vect) std::vector<boost::shared_ptr<RDKit::MolSanitizeException>>;
 
 %newobject RDKit::MolOps::renumberAtoms;
 %newobject RDKit::MolOps::removeHs;
 %newobject RDKit::MolOps::addHs;
+%ignore RDKit::MolOps::detectChemistryProblems;
 %include <GraphMol/MolOps.h>
 %ignore RDKit::MolOps::sanitizeMol(RWMol &,unsigned int &,unsigned int &);
 
@@ -53,4 +54,12 @@
     }
     return static_cast<int>(opThatFailed);
   };
+  std::vector<boost::shared_ptr<RDKit::MolSanitizeException>> detectChemistryProblems(RDKit::ROMol &mol,int sanitizeOps=RDKit::MolOps::SANITIZE_ALL){
+    std::vector<boost::shared_ptr<RDKit::MolSanitizeException>> res;
+    auto probs = RDKit::MolOps::detectChemistryProblems(mol,sanitizeOps);
+    for(const auto &exc_ptr : probs) {
+      res.push_back(boost::shared_ptr<RDKit::MolSanitizeException>(exc_ptr->copy()));
+    }
+    return res;
+  };
 %}
diff --git a/Code/JavaWrappers/SanitException.i b/Code/JavaWrappers/SanitException.i
index 42f38d2a0..eb8aee976 100644
--- a/Code/JavaWrappers/SanitException.i
+++ b/Code/JavaWrappers/SanitException.i
@@ -38,3 +38,68 @@
 
 
 %include <GraphMol/SanitException.h>
+#ifdef SWIGJAVA
+// support upcasting from MolSanitizeException to the other exception types so that
+// we can do something with the output of detectChemistryProblems()
+
+// approach from: http://www.swig.org/Doc3.0/Java.html#Java_adding_downcasts
+%exception RDKit::AtomSanitizeException::dynamic_cast(RDKit::MolSanitizeException) {
+  $action
+    if(!result){
+      jclass excep = jenv->FindClass("java/lang/ClassCastException");
+      if (excep) {
+        jenv->ThrowNew(excep, "dynamic_cast exception");
+      }
+    }
+}
+%extend RDKit::AtomSanitizeException {
+    static RDKit::AtomSanitizeException *dynamic_cast(RDKit::MolSanitizeException *mse){
+        return dynamic_cast<RDKit::AtomSanitizeException *>(mse);
+    }
+};
+
+%exception RDKit::AtomValenceException::dynamic_cast(RDKit::MolSanitizeException) {
+  $action
+    if(!result){
+      jclass excep = jenv->FindClass("java/lang/ClassCastException");
+      if (excep) {
+        jenv->ThrowNew(excep, "dynamic_cast exception");
+      }
+    }
+}
+%extend RDKit::AtomValenceException {
+    static RDKit::AtomValenceException *dynamic_cast(RDKit::MolSanitizeException *mse){
+        return dynamic_cast<RDKit::AtomValenceException *>(mse);
+    }
+};
+
+%exception RDKit::AtomKekulizeException::dynamic_cast(RDKit::MolSanitizeException) {
+  $action
+    if(!result){
+      jclass excep = jenv->FindClass("java/lang/ClassCastException");
+      if (excep) {
+        jenv->ThrowNew(excep, "dynamic_cast exception");
+      }
+    }
+}
+%extend RDKit::AtomKekulizeException {
+    static RDKit::AtomKekulizeException *dynamic_cast(RDKit::MolSanitizeException *mse){
+        return dynamic_cast<RDKit::AtomKekulizeException *>(mse);
+    }
+};
+
+%exception RDKit::KekulizeException::dynamic_cast(RDKit::MolSanitizeException) {
+  $action
+    if(!result){
+      jclass excep = jenv->FindClass("java/lang/ClassCastException");
+      if (excep) {
+        jenv->ThrowNew(excep, "dynamic_cast exception");
+      }
+    }
+}
+%extend RDKit::KekulizeException {
+    static RDKit::KekulizeException *dynamic_cast(RDKit::MolSanitizeException *mse){
+        return dynamic_cast<RDKit::KekulizeException *>(mse);
+    }
+};
+#endif
\ No newline at end of file
diff --git a/Code/JavaWrappers/csharp_wrapper/GraphMolCSharp.i b/Code/JavaWrappers/csharp_wrapper/GraphMolCSharp.i
index b199b3e8a..50b79a315 100644
--- a/Code/JavaWrappers/csharp_wrapper/GraphMolCSharp.i
+++ b/Code/JavaWrappers/csharp_wrapper/GraphMolCSharp.i
@@ -178,6 +178,10 @@ typedef unsigned long long int	uintmax_t;
 %shared_ptr(RDKit::QueryBond)
 %shared_ptr(RDKit::QueryOps)
 %shared_ptr(RDKit::MolSanitizeException)
+%shared_ptr(RDKit::AtomSanitizeException)
+%shared_ptr(RDKit::AtomValenceException)
+%shared_ptr(RDKit::AtomKekulizeException)
+%shared_ptr(RDKit::KekulizeException)
 %shared_ptr(RDKit::SmilesParseException)
 %shared_ptr(RDKit::RingInfo)
 %shared_ptr(RDKit::ChemicalReaction)
diff --git a/Code/JavaWrappers/gmwrapper/GraphMolJava.i b/Code/JavaWrappers/gmwrapper/GraphMolJava.i
index 1d88dd843..19e7feb64 100644
--- a/Code/JavaWrappers/gmwrapper/GraphMolJava.i
+++ b/Code/JavaWrappers/gmwrapper/GraphMolJava.i
@@ -130,6 +130,10 @@ typedef unsigned long long int	uintmax_t;
 %shared_ptr(RDKit::QueryBond)
 %shared_ptr(RDKit::QueryOps)
 %shared_ptr(RDKit::MolSanitizeException)
+%shared_ptr(RDKit::AtomSanitizeException)
+%shared_ptr(RDKit::AtomValenceException)
+%shared_ptr(RDKit::AtomKekulizeException)
+%shared_ptr(RDKit::KekulizeException)
 %shared_ptr(RDKit::SmilesParseException)
 %shared_ptr(RDKit::MolPicklerException)
 %shared_ptr(RDKit::RingInfo)
diff --git a/Code/JavaWrappers/gmwrapper/src-test/org/RDKit/BasicMolecule2Tests.java b/Code/JavaWrappers/gmwrapper/src-test/org/RDKit/BasicMolecule2Tests.java
index 0e0974b6a..bc90cff97 100644
--- a/Code/JavaWrappers/gmwrapper/src-test/org/RDKit/BasicMolecule2Tests.java
+++ b/Code/JavaWrappers/gmwrapper/src-test/org/RDKit/BasicMolecule2Tests.java
@@ -1,5 +1,4 @@
 /* 
- * $Id: BasicMolecule2Tests.java 131 2011-01-20 22:01:29Z ebakke $
  *
  *  Copyright (c) 2010, Novartis Institutes for BioMedical Research Inc.
  *  All rights reserved.
@@ -175,6 +174,31 @@ public class BasicMolecule2Tests extends GraphMolTest {
 		assertEquals(3,mvv.get(0).size());
 	}
 
+	@Test public void testDetectChemistryProblems() {
+		ROMol m2;
+		m2 = RWMol.MolFromSmiles("CFCc1cc1",0,false);
+		MolSanitizeException_Vect res;
+		res = RDKFuncs.detectChemistryProblems(m2);
+		assertEquals(res.size(),2);
+		assertEquals(res.get(0).getType(),"AtomValenceException");
+		assertEquals(res.get(1).getType(),"KekulizeException");
+		// fun with swig and C++ inheritance:
+		KekulizeException ke = KekulizeException.dynamic_cast(res.get(0));
+		assertNull(ke);
+		ke = KekulizeException.dynamic_cast(res.get(1));
+		assertNotNull(ke);
+		assertEquals(ke.getAtomIndices().size(),3);
+		assertEquals(ke.getAtomIndices().get(0),3);
+		assertEquals(ke.getAtomIndices().get(1),4);
+		assertEquals(ke.getAtomIndices().get(2),5);
+
+		AtomValenceException ave = AtomValenceException.dynamic_cast(res.get(0));
+		assertNotNull(ave);
+		assertEquals(ave.getAtomIdx(),1);
+
+	}
+
+
 	public static void main(String args[]) {
 		org.junit.runner.JUnitCore.main("org.RDKit.BasicMolecule2Tests");
 	}
diff --git a/Code/JavaWrappers/gmwrapper/src-test/org/RDKit/BasicMoleculeTests.java b/Code/JavaWrappers/gmwrapper/src-test/org/RDKit/BasicMoleculeTests.java
index 08d1d687f..e585ad7f9 100644
--- a/Code/JavaWrappers/gmwrapper/src-test/org/RDKit/BasicMoleculeTests.java
+++ b/Code/JavaWrappers/gmwrapper/src-test/org/RDKit/BasicMoleculeTests.java
@@ -1,5 +1,4 @@
 /*
- * $Id: BasicMoleculeTests.java 131 2011-01-20 22:01:29Z ebakke $
  *
  *  Copyright (c) 2010, Novartis Institutes for BioMedical Research Inc.
  *  All rights reserved.