11. Thermochemistry of olefins, carbonyl compounds and imines |
607 |
109.The regression analysis of equation 4b for the 2,2-dimethoxyalkanes is (kJ mol 1):
Hf n-RC(OMe)2CH3, l D 24.14nc 340.2.
110.The enthalpy of formation of 2-hexanone was estimated from Table 4. The enthalpy of formation of 2,2-dimethoxyhexane was estimated from Reference 109.
111.The enthalpy of formation of cyclopropanone, n D 2, is taken as that suggested by Liebman and Greenberg56, accepting the analysis of the appearance energy threshold ion measurements of the fragmentation of cyclopropanone radical cation into ethylene radical cation C carbon monoxide, H. J. Rodrigues, J.-C. Chang and T. F. Thomas, J. Am. Chem. Soc., 98, 2027 (1976), but using more recent ancillary data.
112.G. Wolf, Helv. Chim. Acta, 55, 1446 (1972). We have chosen the enthalpies of formation of the n D 5 8 cycloalkanones from this source, rather than from the archival value by Pedley, so as to provide a greater uniformity of origin for the chosen data. In any case, that the values are the same within the proferred error bars suggests little difference will arise by using the data from either source. For the same reason of uniformity of data, we have also chosen the value for the n D 4 species from Wolf rather than from J. Rocekˇ and A. E. Radkowsky, J. Am. Chem. Soc., 95, 7123 (1973), or by estimating it by assuming that the following reaction is thermoneutral:
PhCH CH2 2CO C C3H8 ! PhPr-i C CH2 3CO
using the phenylcyclobutanone data from R. R. Krall and J. D. Roberts, Am. Chem. Soc., Div. Petr. Chem. Symp., B-63 (1958). In both of the latter cases, a nearly 10 kJ mol 1 discrepancy is incurred relative to Wolf’s data.
113.Reference 111 employed ionization and appearance energy measurements, and not the ‘conventional’ combustionor solution-phase reaction calorimetry used to obtain most enthalpies of formation reported in the literature.
114.Prof. Ernest L. Eliel, personal communication to the authors.
115.It is not obvious how to deconvolute the above reasoning with one that considers the 7-isomer as having the carbonyl part of a 5-membered ring and the 2-isomer as having it part of a less strained 6-membered ring.
116.P. Muller,¨ J. Blanc and D. Lenoir, Helv. Chim. Acta, 65, 1212 (1982) cite an unpublished gasphase enthalpy of formation of this species.
117.We note the earlier paper by Becker and Roth65 that presented a value for bicyclo[2.2.2]octanone (herein named endo-ethylenecyclohexanone) that differed from the just-cited more recent one116 by ca 4 kJ mol 1.
118.J. S. Chickos, D. G. Hesse, J. F. Liebman and S. Y. Panshin, J. Org. Chem., 54, 3424 (1988).
119.D. Paoli, J.-C. Garrigues and H. Patin, Compt. Rend., C268, 780 (1969).
120.J.-L. M. Abboud, P. Jimenez,´ M. V. Roux, C. Turrion,´ C. Lopez-Mardomingo and G. Sanz, J. Chem. Thermodyn., 24, 217 (1992).
121.J.-L. M. Abboud, P. Jimenez,´ M. V. Roux, C. Turrion´ and C. Lopez-Mardomingo, J. Chem. Thermodyn., 21, 859 (1989).
122.This value was obtained by summing the temperature-uncorrected enthalpy of fusion of benzophenone and the archival enthalpy of formation of the solid.
123.We use here the gas-phase data of M. Colomina, P. Jimenez,´ M. V. Roux and C. Turrion,´ J. Chem. Thermodyn., 19, 1139 (1987), although the difference for the standard enthalpies of formation of the solid trimethylbenzoic acids is again in the reverse direction to that of the acetophenones, 17.8 š 1.6 kJ mol 1.
124.What adds to our suspicion is that the steric effect of Me and COOH in substituted benzenes are so comparable: M. Colomina, C. Turrion,´ P. Jimenez,´ M. V. Roux and J. F. Liebman, Struct. Chem., 5, 141 (1994). It seems very unlikely that the steric effects of COMe and COOH could be that different.
125.J. F. Liebman, Struct. Chem., 3, 449 (1992).
126.J. S. Chickos, D. G. Hesse and J. F. Liebman, J. Org. Chem., 54, 5250 (1989).
127.We recall the use of the substituent constants for the relevant >CO and X groups from the preceding reference for generating near-additivity for enthalpies of vapourization of many other types of COX species, J. F. Liebman and J. S. Chickos, Struct. Chem., 1, 501 (1990).
128.We note that even Chemical Abstracts persists in calling the intramolecularly hydrogen-bonded isomer CH3C(OH)DCHCOCH3 pentane-2,4-dione and leaves the diketone compound of interest in the current context without a name or even a registry number.
608 |
Suzanne W. Slayden and Joel F. Liebman |
129.J. M. Hacking and G. Pilcher, J. Chem. Thermodyn., 11, 1015 (1979).
130.H. Y. Afeefy and J. F. Liebman, unpublished analysis, find it useful to affix to the name 
(derived from the Arabic 
meaning ‘as it is written’ or else the transliterated Km from ‘K’makotep’).
131.G. Pilcher, O. G. Parchment, I. H. Hillier, F. Heatley, D. Fletcher, M. A. V. Ribeiro da Silva, M. L. C. C. H. Ferrao,˜ M. J. S. Monte and F. Jiye, J. Phys. Chem., 97, 243 (1993).
132.Our ignorance is only compounded when the keto and enol groups are stripped off and a comparison is made between the enthalpies of formation of 3,3- and 4,4-dimethylcyclohexene. Pilcher
and coworkers131 chronicle that the former has a higher enthalpy of hydrogenation than the latter by but 4.6 kJ mol 1. In that the solvent was the same for both measurements (glacial AcOH) and that the product is the same (1,1-dimethylcyclohexane), we have lost a plausible ‘excuse’ for the difference of stability of the isomeric dimethylcyclohexane-1,3-diones. Furthermore, the difference of hydrogenation enthalpies between either dimethylcyclohexene and that of cyclohexene in this medium is only 3 kJ mol 1. The profound lack of thermoneutrality of reactions 53 remains disconcerting.
133. Note, as discussed in Reference 8, 1,3-dimethylenecyclohexane is some 10 kJ mol 1 more stable than its 1,4-isomer. The 1,3- and 1,4-dimethylene compounds are stabilized relative to the monomethylene compound by 19 and 9 kJ mol 1, respectively, while the corresponding diketones are stabilized relative to the monoketone by some 7 and 4 kJ mol 1. These results are consonant with the 1,3-bis-sp2 cyclohexanes being more stabilized than their 1,4-counterpart, but electrostatic destabilization affecting the ˇ-diketone and not particularly the bismethylene compound.
134.L. Ruzicka and P. Schlapter,¨ Helv. Chim. Acta, 16, 162 (1933).
135.We must admit, however, that the corresponding formal solid-phase dimerization reaction of cyclopentadecane to cyclotriacontane shows no such near-thermoneutrality, suggestive of unenunciated complications with the study of these large rings.
136.J. F. Liebman, in Fluorine-containing Molecules: Structure, Reactivity, Synthesis and Applications (Eds. J. F. Liebman, A. Greenberg and W. R. Dolbier, Jr.), VCH, New York, 1988.
137.B. J. Smith, J. A. Pople, L. A. Curtiss and L. Radom, Aust. J. Chem., 34, 285 (1992), using calculational theory at the G2 level, provide what has been taken to be a definitive answer, 86 š 10 kJ mol 1. As an example of such enthusiasm applied to more generally substituted, and thus more complicated imines, see M. B. Seasholtz, T. B. Thompson and N. G. Rondan, J. Phys. Chem., 99, 17838 (1995).
138.D. J. DeFrees and W. J. Hehre, J. Phys. Chem., 82, 391 (1978).
139.W. A. Tarasenko, A. A. Tishenov, V. G. Zaikin, V. V. Volkova and L. E. Gulsel’nikov, Izv. Ser. Chim. (Engl. Transl.), 35, 2196 (1986).
140.M. A. Grela and A. J. Colussi, Int. J. Chem. Kinet., 20, 713 (1988).
141.R. A. L. Peerboom, S. Ingemann, N. M. M. Nibbering and J. F. Liebman, J. Chem. Soc., Perkin Trans. 2, 1825 (1990).
142.J. L. Holmes, F. P. Lossing and P. M. Mayer, Chem. Phys. Lett., 198, 211 (1992).
143.See the discussion in Liebman, Campbell and Slayden62.
144.M. R. Ellenberger, R. A. Eades, M. W. Thomsen, W. Farneth and D. A. Dixon, J. Am. Chem. Soc., 101, 7151 (1979).
145.X.-W. An and M. Mansson,˚ J. Chem. Thermodyn., 25, 287 (1983).
146.G. Bouchoux, J.-Y. Salpin, D. Leblanc, C. Alcaraz, O. Dutuit and H. Palm, Rapid Commun. Mass Spectrom., 9, 1195 (1995).
147.K. B. Wiberg, D. Y. Nakaji and K. M. Morgan, J. Am. Chem. Soc., 115, 3527 (1993).
148.It is easy to disparage Reference 141. However, we note that we did not say whether we are
considering (Z)- or (E)-MeCHNMe. Should we wish to invoke calculational results those of Reference 147 we find that reaction 64 is approximately thermoneutral (ca 2 kJ mol 1 discrepancy) as anticipated. However, unlike the isoelectronic 2-butene for which the (E)-isomer is only 4.3 š 1.4 kJ mol 1 more stable than its (Z)-isomer (from experiment), these same literature calculations show that (E)-MeCHNHMe is almost 18 kJ mol 1 more stable than the (Z)-isomer that is implicitly needed for the above reaction. We would thus predict the enthalpy of formation of 1-azacyclopentene to be ca 58 š 14 kJ mol 1 and so the data in Reference 141 is also consistent with the literature experimental data on this new heterocycle.
11. Thermochemistry of olefins, carbonyl compounds and imines |
609 |
149.The earlier reference results in a value of 161.0 š 10.0 kJ mol 1. Undetected, and so uncorrected, hydrolysis and/or polymerization could result in the observed difference.
150.L. M. Jackman and D. I. Packam, Proc. Chem. Soc., 349 (1957).
151.S. W. Benson, F. R. Cruickshank, D. M. Golden, G. R. Haugen, H. E. O’Neal, A. S. Rodgers,
R.Shaw and R. Walsh, Chem. Rev., 69, 279 (1969).
152.We used the theoretical value of the enthalpy of formation of dipropylamine for consistency. The archival experimental value is but 1 kJ mol 1 dissonant.
153.G. Haflinger¨ and L. Steinmann, Angew. Chem., Int. Ed. Engl., 16, 47 (1977). We thank Prof.
G.Haflinger¨ for sending us a copy of L. Steinmann’s doctoral thesis.
154.Following the procedure in Liebman, Campbell and Slayden62, we derived the new υ (sec/prim, tert) enthalpy increment, numerically equal to 65 kJ mol 1.
155.We used the theoretical value of the enthalpy of formation of di-n-butylamine for consistency. The archival experimental value is but 2 kJ mol 1 dissonant.
156.This is derived from reasoning based on the enthalpies of formation of other pairs of EtX and
n BuX, and of n PrX and i PrX species. For example, let us take X D NH2 and CN. For amines, the ethyl/butyl difference is 44.6š 1.4 while for nitriles it is 41.0š 1.5 kJ mol 1. For amines, the isopropyl/n-propyl difference is 13.6 š 0.7 kJ mol 1 while for nitriles it is 10.3 š 1.6 kJ mol 1.
157.G. S. Wayne, G. J. Snyder and D. W. Rogers, J. Am. Chem. Soc., 115, 9860 (1993). In this paper, the enthalpies of formation of the requisite azides were determined by hydrogenation to the amine and estimation of the latter enthalpies of formation. While far less is known about the enthalpies of formation of azides than amines, this approach seems without additional complication or significant error.
158.Were we to relax our restriction to consider solely hydrocarbyl substituents and accept both
benzenoid and non-benzenoid aromatic imines, we would |
find other relevant compounds. |
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For example, there is N-t-butyl-p-nitrobenzaldimine with a |
gas-phase enthalpy of formation |
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of 49.4 š 3.6 kJ mol 1 |
from W. E. Acree, |
Jr., J. J. Kirchner, |
S. A. Tucker, G. Pilcher and |
|
M. D. M. C. R. Ribeiro |
da Silva, J. Chem. |
Thermodyn., 21, |
443 (1989) and N-methyl-7- |
|
(methylamino)-troponimine (misnamed in our principal archive, Reference 16) with a gas-phase enthalpy of formation of 211.2 š 4.2 kJ mol 1. Another relevant species is ammonium murexide with its 100-year-old enthalpy of formation of 1212 kJ mol 1 as chronicled by Domalski. These three compounds are interesting, but it is precisely the non-hydrocarbyl part of these species that confounds simple comparison with other interesting species in this chapter.
159.From the gas-phase ion molecule literature we find the isomeric protonated tropone and protonated benzaldehyde to be nearly isoenergetic, while the parent (i.e. not methylated) tropylium ion is more stable than benzyl cation by ca 50 kJ mol 1; cf S. G. Lias, J. E. Bartmess, J. F. Liebman, J. L. Holmes, R. D. Levin and W. G. Mallard, ‘Gas-Phase Ion and Neutral Thermochemistry’,
J. Phys. Chem. Ref. Data, 17, Supplement 1 (1988).
160.J. J. Kirchner, W. E. Acree, Jr., G. Pilcher and L. Shaofeng, J. Chem. Thermodyn., 18, 793 (1986).
161.I. G. Gut and J. Wirz, Angew. Chem., Int. Ed. Engl., 33, 1153 (1994).
162.We do not have to concern ourselves with aniline-like conjugation of the -electrons of the benzene ring with the nitrogen lone-pair electrons because the - and n-orbitals are geometrically perpendicular and so do not overlap. We also do not concern ourselves with the 5 kJ mol 1 discrepancy in the values of the enthalpy of formation of cyclopentadiene as found in Roth and coworkers54 and that which we take from our major data archive.
163.We note that for the case of keto/enol interconversion, it is simple, useful and remarkably accurate to equate the difference of Gibbs energies in aqueous media of the two tautomers and the difference of enthalpies of formation in the gas; J. R. Keefe and A. J. Kresge, J. Phys. Org. Chem., 5, 575 (1992). We are pleased.