Electronic effects in a prototype push-pull ethylene: a study of rotational barriers in C₄H₄N₄ isomers

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• 作者：Dwyer ; Tammy J. ; Jasien ; Paul G.
• 关键词：Electronic effect ; Push-pull ethylene ; Rotational barrier
• 刊名：Journal of Molecular Structure: THEOCHEM
• 出版年：1996
• 出版时间：April 15, 1996
• 年：1996
• 卷：363
• 期：2
• 页码：139-150
• 全文大小：927 K

文摘

Quantum mechanical calculations of the rotational barriers in the prototype push-pull ethylene 1,1-diamino-2,2-dicyanoethylene (DADCE) and its non-push-pull analogues diaminofumaronitrile (DAFN) and diaminomaleonitrile (DAMN) have been used quantitatively to assess the influence of the push-pull effect. Results for DADCE indicate an in vacuo barrier for CC rotation of 28 kcal mol⁻¹ which decreases in solvents of increasing dielectric strength. The barrier for C-N rotation in DADCE is found to be 8 kcal mol⁻¹ and increases with solvent dielectric strength. The comparable CC barrier connecting DAMN and DAFN is calculated to be > 20 kcal mol⁻¹ higher than the DADCE barrier. Analysis of the conformational energies of DADCE, DAMN, and DAFN gives further evidence for the increased dipolar character and nitrogen lone pair conjugation in DADCE as compared with DAMN and DAFN.