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Differential Effects of Nitrogen Substitution in 5-and 6-Membered Aromatic Motifs
被引:8
作者:
Levandowski, Brian J.
[1
]
Abularrage, Nile S.
[1
]
Raines, Ronald T.
[1
]
机构:
[1] MIT, Dept Chem, Cambridge, MA 02139 USA
关键词:
aromaticity;
cycloaddition;
density functional calculations;
kinetics;
HYPERCONJUGATIVE AROMATICITY;
ALDER;
REACTIVITY;
TETRAZINES;
D O I:
10.1002/chem.202000825
中图分类号:
O6 [化学];
学科分类号:
0703 ;
摘要:
The replacement of carbon with nitrogen can affect the aromaticity of organic rings. Nucleus-independent chemical shift (NICS) calculations at the center of the aromatic pi-systems reveal that incorporating nitrogen into 5-membered heteroaromatic dienes has only a small influence on aromaticity. In contrast, each nitrogen incorporated into benzene results in a sequential and substantial loss of aromaticity. The contrasting effects of nitrogen substitution in 5-membered dienes and benzene are reflected in their Diels-Alder reactivities as dienes. 1,2-Diazine experiences a 1011-fold increase in reactivity upon nitrogen substitution at the 4- and 5-positions, whereas a 5-membered heteroaromatic diene, furan, experiences a comparatively incidental 102-fold increase in reactivity upon nitrogen substitution at the 3- and 4-positions.
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页码:8862 / 8866
页数:5
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