Conformation of Aminals Derived From Arylamines and Methanal

In this thesis, the poly-condensation, which takes place between formaldehyde and ary- lamine under basic conditions, is studied by establishing the structures of the 2:1 adducts (34) and (36) and the cyclic 3:3 adducts (32), (41), (43) and (45) by X-ray crystal structure analysis and spectroscopic methods. The presence of electron-withdrawing substituents ortho or para to the amino group of the arylamine promotes, in some cases, termination of the poly-condensation at the 2:1 adduct stage but the potential stereochemical blocking effect of an electron-donating substituent on the arylamine ortho position does not hinder the formation of higher adducts. The further poly-condensation observed of certain 2:1 adducts bearing electron- withdrawing substituents are interpreted as the result of variations in the nitrogen atom basicity, polarity and solubility. Reaction of those arylamines, which above gave 2:1 adducts, with dimethyl sulphoxide/ phosphorus pentoxide did not yield cyclic 3:3 adducts. The 2:1 adducts isolated show that in the solid state N,N bis-(2-trifluoromethylphenyl)-diaminomethane (36) adopts a skewed conformation around both N-CH2 bonds. The N-CH2 bond is rotated out of the plane of the adjacent phenyl ring to a small extent. The bond angles in the chain linking the phenyl groups are distinctly greater than tetrahedral. The N-CH2 are longer than the N-C(aryl) bonds, similar values for N-C(aryl) bonds have been observed in N,N-dialkylanilines with electron-withdrawing substituents on the phenyl rings. In the trifluoromethyl groups the F-C-F angles are all smaller than tetrahedral. The short H...F distance between the H atoms on N(A) and N(B) and the F atoms of the adjacent CF3 may represent intramolecular hydrogen bonding since there is no intermolecular hydrogen bonding. The cyclic 3:3 adducts isolated all adopt the twin-chair conformation with the substituents in the aae conformation. The N-C(axial) bonds in the o-OMe and p-OMe compounds are bent outwards by 15-2