Title: Substituted Phenyl 2-Thiophenecarboxylates and Benzoates: Synthesis, NMR Spectra, and Aromaticity Index
Abstract:comparison of the indices of aromaticity, with that of benzene set as 1, the values of 0.46, 0.59, and 0.75 are assigned to furan, pyrrole, and thiophene, respectively. These values are calculated by ...comparison of the indices of aromaticity, with that of benzene set as 1, the values of 0.46, 0.59, and 0.75 are assigned to furan, pyrrole, and thiophene, respectively. These values are calculated by the ring currents measured by the chemical shifts of the protons. 2 In contrast, the aromaticity indices derived from the bond length and the number of π electrons in the ring are very close in value: benzene, 1; thiophene, 0.93; pyrrole, 0.91; furan, 0.87. 3 Among thiophene, pyrrole, and furan, which are commonly encountered as 5-membered heterocycles, thiophene is considered most similar to benzene, and the relative aromaticity of thiophene ranges from 0.55 to 0.93, when the aromaticity of benzene is set at 1. Recently, a new order of values with benzene set at 100 was reported for furan (53), thiophene (81.5), and pyrrole (85). 4 It is not certain why the order between pyrrole and thiophene switched. Our continuous study on the aromaticities of five-membered heterocyclic compounds 5,6 led us to the preparation of m- and p-substituted phenyl esters of 2-thiophenecarboxylic acid (2-thienoate) to examine the effect of the substituents on the phenyl ring on the chemical shift of the H and C atoms of the thiophene ring.Read More
Publication Year: 2000
Publication Date: 2000-01-01
Language: en
Type: article
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Cited By Count: 3
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