The Melting Point Alternation in ,-Alkanedithiols

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• 作者：Venkat R. Thalladi ; Roland Boese ; and Hans-Christoph Weiss
• 刊名：Journal of the American Chemical Society
• 出版年：2000
• 出版时间：February 16, 2000
• 年：2000
• 卷：122
• 期：6
• 页码：1186 - 1190
• 全文大小：110K
• 年卷期：v.122,no.6(February 16, 2000)
• ISSN：1520-5126

文摘

RC="/images/gifchars/alpha.gif" BORDER=0>,rs/omega.gif" BORDER=0 >-Alkanedithiols show an alternation in their melting points with even members exhibitingsystematically higher melting points than odd members. In this study, single crystals of the first nine membersof rs/alpha.gif" BORDER=0>,rs/omega.gif" BORDER=0 >-alkanedithiols (HS-(CH₂)_n-SH, n = 2-10) have been grown in situ using a miniature zone meltingprocedure, and their X-ray analyses have been performed. The structural similarities and differences betweeneven and odd members have been analyzed based on the packing arrangements of hydrocarbon chains and SHfunctionalities. Whereas the hydrocarbon chains maintain an intergrooving pattern, the SH groups associate inan antiparallel fashion in both the members. The SH groups do not form hydrogen bonds. In the even membersthe molecules are offset along their length, whereas such an offset is not observed in the odd members. Thedensities of even members are systematically higher than those of odd members and show an alternatingtrend. Using a simple geometrical model, describing even and odd members as modified parallelograms andtrapezoids, respectively, the density features of the packing patterns in both the members are illustrated. Themelting point alternation in dithiols is attributed to the geometry allowed or forbidden molecular offset towarda higher packing density.