Abstract
Detailed X-ray crystallographic investigation of the reactive α- and the unreactive γ-polymorphs ofo-ethoxy cinnamic acid has been carried out along with that of the photodimer, α-truxillic acid. The molecule is quite planar in the α-form, but in the γ-form, the side groups deviate significantly from the plane of the benzene ring. The carboxylic groups form normal cyclic hydrogen bonds in the α-form and near-symmetric hydrogen bonds in the γ-form. The infrared spectrum of the α-form shows the characteristic features of the cyclic dimer, but that of the γ-form is entirely different, marked by the absence of the O-H stretching band in the 3000 cm-1 region. Charge density analysis throws some light on the structure and reactivity of the molecule in the two forms. The near-symmetric hydrogen bond in the γ-form is ionic and appears to restrict conjugation by way of distorting the molecule. This unusual feature keeps the cinnamoyl double bonds away from each other, rendering it photochemically unreactive. In the α-form, however, the double bonds have a closer approach. The cyclobutyl ring of the photodimer consists of weak single bonds, with the new pair being slightly longer.
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References
Cohen M D, Schmidt G M J and Sonntag F I 1964J. Chem. Soc. 2000
Enkelmann V, Wegner G, Novak K and Wagener K B 1993J. Am. Chem. Soc. 115 10390
Jeffrey G A and Piniella J F (eds) 1991The application of charge density research to chemistry and drug design (New York: Plenum)
Ortmann I, Werner St and Kruger C 1992J. Am. Chem. Soc. 114 5048
Madsen D, Flensburg C and Larsen S 1998J. Phys. Chem. A102 2177
Kulkarni G U, Kumardhas P and Rao CNR 1998Chem. Mater. 10 3498
Furniss B S, Hannaford A S, Smith P W G and Tatchell A R (eds) 1989Vogel’s textbook of practical organic chemistry (Harlow, Essex: Addison Wesley-Longman)
Siemens Analytical X-ray Instruments Inc. 1995 Madison, Wisconsin, USA
SHELXTL 1995 (Silicon Graphics version) Siemens Analytical X-ray Instruments Inc. Madison, Wisconsin, USA
Allen F H, Kennard O, Watson D G, Brammer L, Orpen A G and Taylor R 1987J. Chem. Soc., Perkin Trans. II S1
Schomaker V and Trueblood K N 1998Acta Cryst. B54 507
Hirshfeld H L 1976Acta Crystallogr. A32 239
Hansen N K and Coppens P 1978Acta Crystallogr. A34 909
Koritsansky T, Howard S T, Richter T, Mallinson P R, Su Z and Hansen N K 1995 XD — A computer program package for multipole refinement and analysis of charge densities from diffraction data (Cardiff, Glasgow, Buffalo, Nancy, Berlin); xd-user@chemie.fu-berlin.de
Cremer D and Kraka E 1984Croat. Chem. Acta 57 1259
Collard K and Hall G G 1977Int. J. Quantum Chem. 12 623
Bader R F W and Essen H 1984J. Chem. Phys. 80 1943
Naradelli M 1983Comput. Chem. 7 95
Bellamy L J 1975The infrared spectra of complex molecules 3rd edn (London: Chapman and Hall)
Rao CNR and Ferraro J R 1970Spectroscopy in inorganic chemistry (New York: Academic Press) vol. 1
Braunholtz J T, Hall G E, Mann F G and Sheppard N 1959J. Chem. Soc. 868
Blinc R and Hadzi D 1960Spectrochem. Acta 16 852
Coppens P 1994Annu. Rev. Phys. Chem. 43 663
Morrison R T and Boyd R N 1989Organic chemistry 5th edn (New Delhi: Prentice Hall-India)
Mallinson P R, Wozniak K, Smith G T and McCormack K L 1997J. Am. Chem. Soc. 119 11502
Bader R F W 1990Atoms in molecules — A quantum theory (Oxford: Clarendon)
Angermund K, Claus K H, Goddard R and Kruger C 1985Angew. Chem., Intl. Ed. Engl. 24 237
Irngartinger H and Strack S 1998J. Am. Chem. Soc. 120 5818
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Gopalan, R.S., Kulkarni, G.U. An investigation of the photo-reactive and unreactive polymorphs ofo-ethoxy cinnamic acid and of its photodimer. J Chem Sci 113, 307–324 (2001). https://doi.org/10.1007/BF02708650
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DOI: https://doi.org/10.1007/BF02708650