Why does deuterium substitution lead to the contraction of X···π distance? Origin of the reverse Ubbelohde effect in XH···π interaction
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The H/D/T geometrical isotope effect (GIE) on XH···π interaction in XH···benzene (X = CH3, OH, and NH2) complexes is analyzed by MP2 level of multi-component molecular orbital calculations, which can take account of nuclear quantum nature. The distances between X atom and center of the benzene ring in XD···benzene and XT···benzene complexes are found to be shorter than that in XH···benzene complex, which shows a different trend in the conventional hydrogen-bonded complexes. Such reverse Ubbelohde effect in XH···benzene complexes is explained by the cooperative effect of two kinds of GIEs: (1) primary GIE on the covalent X–H bond and (2) secondary GIE on the H···π distance. We have clearly revealed that the primary GIE is dominant in the GIE of XH···π complexes.
KeywordsGeometrical isotope effect (GIE) XH···π interaction Ubbelohde effect Multi-component molecular orbital calculation Nuclear quantum nature
The part of the present study was supported by Grant-in-aid Scientific Research by Ministry of Education, Culture, Sports, Science and Technology, Japan (Kakenhi) (Grant Nos. 25104721, 26102539, and 26620013 for M.T.). The part of the computations was performed using Research Center for Computational Science, Okazaki, Japan.
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