Abstract
Conformation of dimer (dihydroxydiphenyl methane) was investigated by the CNDO/2 method. The stable conformation of the above compound is a roof-type model with respect to the two benzene rings connected by the methylene group, and the most stable structure is a roof-type model with an intermolecular hydrogen bond between the two OH groups. The intra-molecular hydrogen bond energy was estimated to be 4. 2 kcal/mol by the CNDO/2 method.
On the other hand, the conformation of trimer was investigated by the same method. Trimer has fundamentally two conformations with respect to the three benzene rings. The first and third benzene rings connected to the second benzene ring are placed at the opposite side (trans-type) and at the same side (cis-type), respectively. The most stable model is trans-type and has two intra-molecular hydrogen bonds among the three OH groups. However, the cis-type model with two intra-molecular hydrogen bonds is the second stable one. The energy difference between the above two models is about 0.8 kcal/ mol. The electron charge density of the H atom of OH group participating in the intra-molecular hydrogen bond systems is decreased as the intra-molecular hydrogen bond becomes longer. This result suggests an increase of acidity of the higher molecular weight phenol novolac oligomer.
