Equilibrium vs Ground-State Planarity of the CONH Linkage

详细信息    查看全文

• 作者：Jean Demaison ; Attila G. Cs&aacute ; sz&aacute ; r ; Isabelle Kleiner ; Harald M//pubs.acs.org/images/gifchars/oslash.gif" border="0">llendal
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：April 5, 2007
• 年：2007
• 卷：111
• 期：13
• 页码：2574 - 2586
• 全文大小：132K
• 年卷期：v.111,no.13(April 5, 2007)
• ISSN：1520-5215

文摘

Planarity of the XC(=)NHY linkage has been investigated in unprecedented detail in a number of relativelysimple compounds, including formamide (X = Y = H), acetamide (X = CH₃, Y = H), urea (X = NH₂, Y= H), carbamic acid (X = OH, Y = H), and methyl carbamate (X = OCH₃, Y = H). Reliable estimates ofthe equilibrium structures of formamide, cyanamide, acetamide, urea, carbamic acid, methylamine, dimethylether, and methyl carbamate are derived, mostly for the first time. It is shown that formamide, consideredprototypical for the amide linkage, is not typical as it has a planar equilibrium amide linkage correspondingto a single-minimum inversion potential around N. In contrast, several molecules containing the CONH linkageseem to have a pyramidalized nitrogen at equilibrium and a double-minimum inversion potential with a verysmall inversion barrier allowing for an effectively planar ground-state structure. Observables of rotationalspectroscopy, including ground-state inertial defects, quadrupole coupling and centrifugal distortion constants,and dipole moment components, as well as equilibrium C=O and C-N bond lengths are reviewed in theirability to indicate the planarity of the effective and possibly the equilibrium structures.