G2ab initio calculations on three-membered rings: Role of hydrogen atoms

✍ Scribed by Alcam�, M.; M�, O.; Y��ez, M.

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 344 KB
• Volume: 19
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/(sici)1096-987x(19980715)19:9<1072::aid-jcc8>3.0.co;2-n

✦ Synopsis

G2 ab initio calculations on all ABX three-membered rings

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. TMRs that can be derived from cyclopropane by systematic substitution of the -CH groups by -NH or -O groups have been performed. Our results show 2 that the decrease in the A-B bond length as the electronegativity of X increases is significantly larger than that found for the corresponding acyclic analogs. In general, a systematic substitution of the -CH groups of cyclopropane by 2 -NH or -O groups implies significant geometric changes that are not reflected in a parallel change of the corresponding conventional ring strain energy Ž . CRSE . When the electronegativity of the groups forming the TMR increases the effect on the CRSE of the system is small, although the charge delocalization inside the ring decreases. The near constancy of the CRSE along the series can be explained in terms of the charge redistribution of the system where the -CH 2 groups play a crucial role. There are, however, significant changes in the hydrogenation energies of the TMR investigated; our results show that, when in an ABX three-membered ring, the electronegativity of X increases the hydrogenation energy of A-B bond decreases and vice versa.