Molecular structure of caffeine as determined by gas electron diffraction aided by theoretical calculations

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• 作者：Toru Egawa ; Akemi Kamiya ; Hiroshi Takeuchi ; Shigehiro Konaka
• 关键词：Caffeine ; Molecular structure ; Gas electron diffraction ; MP2 calculations ; DFT calculations
• 刊名：Journal of Molecular Structure
• 出版年：2006
• 期刊代码：62_00222860
• 类别：ch
• 出版时间：15 December 2006
• 卷：825
• 期：1-3
• 页码：151-157
• 文件大小：306 K

摘要

The molecular structure of caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) was determined by means of gas electron diffraction. The nozzle temperature was 185 °C. The results of MP2 and B3LYP calculations with the 6-31G^** basis set were used as supporting information. These calculations predicted that caffeine has only one conformer and some of the methyl groups perform low frequency internal rotation. The electron diffraction data were analyzed on this basis. The determined structural parameters (r_g and _α) of caffeine are as follows: <r(NC)_ring> = 1.382(3) Å; r(CC) = 1.382(!90;) Å; r(CC) = 1.446(18) Å; r(CN) = 1.297(11) Å; <r(NC_methyl)> = 1.459(13) Å; <r(CO)> = 1.206(5) Å; <r(CH)> = 1.085(11) Å; N₁C₂N₃ = 116.5(11)°; N₃C₄C₅ = 121. 5(13)°; C₄C₅C₆ = 122.9(10)°; C₄C₅N₇ = 104.7(14)°; N₉–C₄=C₅ = 111.6(10)°; <NCH_methyl> = 108.5(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3σ) referring to the last significant digit; left arrow in parentheses means that this parameter is bound to the preceding one.