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Stereoelectronic Properties of Tetrahedral Species Derived from Carbonyl Groups. Ab initio study of aminodihydroxymethane, CH(OH) 2 NH 2 , a model tetrahedral intermediate in amide hydrolysis
Author(s) -
Lehn JeanMarie,
Wipff Georges
Publication year - 1978
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19780610410
Subject(s) - chemistry , antibonding molecular orbital , hyperconjugation , lone pair , ab initio , crystallography , bond length , stereochemistry , single bond , alkane stereochemistry , molecule , crystal structure , group (periodic table) , atomic orbital , organic chemistry , physics , quantum mechanics , electron
An ab initio theoretical study of all fifteen fully staggered conformations of aminodihydroxymethane, CH(OH) 2 NH 2 has been performed. Optimization of the CO and CN bond lengths, population analyses and orbital localisation reveal the presence of marked conformation dependent stereoelectronic effects which influence bond lengths and overlap populations. These effects may be parametrized as a function of number and nature of antiperiplanar ( app ) oriented electronic lone pairs (1p) and polar bonds. In a YCX fragment an app orientation between a lone pair on Y and the CX bond increases the length and weakens the CX bond, shortens and strengthens the CY bond. Thus a CX (X O, N) bond of CH(OH) 2 NH 2 is longest and weakest when: (i) it is app to two vicinal lp's; (ii) the X 1p's are not app to a vicinal polar bond; (iii) the conformation of the molecule has as many axially oriented lp's as possible. Results (i) and (ii) agree with a simple hyperconjugation picture involving interaction between an electronic 1p and an app oriented antibonding bond orbital σ* (CX). Bond properties, relative energies and effects on reactivity of the tetrahedral species are discussed, as well as their relations to experimental results on the cleavage of tetrahedral intermediates and to enzyme catalysis.