| Abstract: | A comparative study of borazine ( 0 ) and six methyl borazines ( 1 to 6 ) has been conducted by NMR. It becomes evident that the chemical shift of N? CH3 protons hardly varies between mono-, di- and tri-N-methyl borazines, whereas this parameter undergoes a strong change (in all 0·21 ppm, to high field) when one passes from N-trimethyl borazine (HB? NCH3)3 to hexamethyl borazine (CH3B? NCH3)3 through a gradual substitution on the three boron atoms ( 3, 4, 5 and 6 ). Moreover, a systematic variation of the parameter δ has been found between compounds 3, 4 and 5 for the protons which keep precisely the same immediate environment. A qualitative interpretation of this experimental result is proposed in terms of electronic effects general to the hexagonal planar boron/nitrogen ring which characterises these molecules. |
