The boronhyphen;11 quadrupole coupling constants of the simple aliphatic symmetrical trialkylboranes determined at 77deg;K are primarily a function of the number of agr;hyphen;carbonmdash;hydrogen bonds in these compounds. The average value ofe2Qqzzin triethyl, trihyphen;nhyphen;propyl, and trihyphen;nhyphen;butylborane is 125plusmn;4 kc/sec higher than that in trimethylborane. The quadrupole coupling constant in trihyphen;isopropylborane is increased an additional 249plusmn;4 kc/sec above the value in the agr;hyphen;methylene compounds. The agr;hyphen;secondary hydrogen isotope effect in trimethylborane is to increasee2Qqzzby 28plusmn;4 kc/sec. However, there is no bgr;hyphen;secondary hydrogen isotope effect in trihyphen;isopropylborane within the limits of experimental error. These results, the proton high resolution NMR spectra, and the available chemical measures of the Lewis acidity of these compounds, are in excellent agreement with classical carbonmdash;hydrogen bond delocalization theory.
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