Benzoic acid, molecular structure

Ultraviolet spectra of benzoic acid in sulphuric acid solutions, published by Hosoya and Nagakura (1961), show a considerable medium effect on the spectrum of the unprotonated acid, but a much smaller one in concentrated acid. The former is probably connected with a hydrogen-bonding interaction of benzoic acid with sulphuric acid which is believed to be responsible for a peculiarity in the activity coefficient behaviour of unprotonated benzoic acid in these solutions (see Liler, 1971, pp. 62 and 129). The absence of a pronounced medium effect on the spectra in >85% acid is consistent with dominant carbonyl oxygen protonation. In accordance with this, Raman spectra show the disappearance in concentrated sulphuric acid of the carbonyl stretching vibration at 1650 cm (Hosoya and Nagakura, 1961). Molecular orbital calculations on the structure of the carbonyl protonated benzoic acid have also been carried out (Hosoya and Nagakura, 1964). 

The single crystal structure of benzoic acid has been reported [52]. In its crystal, the molecule is approximately planar, but distances of0.042 A and 0.068 A displace the carboxylate carbon and one of its oxygen atoms, respectively, from the mean plane. The structure is characterized by the existence of hydrogen-bonded molecular dimers in the unit cell. 

Although the motion of protons does not lead to electrical conduction in the case of benzoic acid, electronic and even ionic conductivity can be found in other molecular crystals. A well-studied example of ionic conduction is a film of polyethylene oxide (PEO) which forms complex structures if one adds alkaline halides (AX). Its ionic conductivity compares with that of normal inorganic ionic conductors (log [cr (Q cm)] -2.5). Other polymers with EO-units show a similar behavior when they are doped with salts. Lithium batteries have been built with this type of... 

Write the structure and calculate the molecular weight of (a) lauric acid, C12H2402, and (b) benzoic acid, C7H602. 

As a consequence of the close-packing principle, chemically different molecules with similar shape and volume should have identical crystal structures [27]. Substances forming mixed crystals must be isomorphous (i.e., not only must they have an identical space group and the same number of molecules, but also a similar molecular packing), otherwise there will be a discontinuity in their solubility curve [5]. For example, benzoic acid and isopropylbenzene, in spite of the similarity in... 

Figure 3.11 Structures of (a) [Sm2L6(MeOH)4] (HL = benzoic acid) and (b) [Pt2L6(H20)3] (HL = acetic acid) [RE, black O, grey C, white H, omitted]. (Redrawn from the CIF files of U.R Singh, R. Kumar and S. Upreti, Synthesis, structural, photophysical and thermal studies of benzoate bridged Sm(III) complexes, Journal of Molecular Structure, 831 (1-3), 97-105, 2007 [56] and D. Deiters and G. Meyer, Synthesis and crystal structure of praseodymium propionate trihydrate, Pr(CH3CH2C00)3(H20)3, Zeitschrift filr Anorganische und Allgemeine Chemie, 622 (2), 325-328, 1996 [57].)...

Kim, K.H. and Martin, Y.C. (1991b). Direct Prediction of Linear Free Energy Substituent Effects from 3D Structures Using Comparative Molecular Field Analysis. 1. Electronic Effects of Substituted Benzoic Acids. J.Org.Chem, 56,2723-2729. 

Maccari R, Ottana R, Ciurleo R et al (2009) Structure-based optimization of benzoic acids as inhibitors of protein tyrosine phosphatase IB and low molecular weight protein tyrosine phosphatase. ChemMedChem 4 957-962... 

The two models have recently come into sharp contrast since they have both been applied to the analysis of the same INS spectrum of benzoic acid [51,53]. The molecular structure of this system is shown in Fig. 9.13. These are the only INS data on O-H-O bonds to be fully analysed using the phonon assisted tunnelling model. However, it is probable that the INS spectra of most systems could be subjected to a similar analysis. 

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