Heats of vaporization and gaseous heats of formation of some five- and six-membered ring alkenes

Abstract

Dc,pcrriritetti c!f Clr~ttti.si~:\*, Utri~r~'siiy oJ'Hor,.siott. Horr.siori, TX 7700-1, U . S . A Received January 16, 1979 RICHARD FUCHS and L. ALAN PEACOCK. Can. J. Chem. 57.2302Chem. 57. ( 1979. The heats of vaporization of I-methylcyclopentene, 3-methylcyclopentene, ethylidenecyclopentane, 1-ethylcyclopentene, methylenecyclohexane, allylcyclopentane, vinylcyclohexane, ethylidenecyclohexane, allylcyclohexane, 3,3-diethylpentane, 2,2,4,4-tetramethylpentane, and trnns-2,2,5,5-tetramethyl-3-hexene have been measured by the gas chromatography -calorimetry method. These values have been combined with previously reported liquid heats of formation to give gaseous values of AH,. The results indicate that the internal double bond is favored by about 0.5 kcal over the exo in both 5-and 6-membered rings, but the endo-exo differences are much smaller than previously believed. Several of the liquid heat capacities that were measured were not well predicted by group additivity schemes.RICHARD FUCHS et L. ALAN PEACOCK. Can. J. Chem. 57.2302Chem. 57. (1979. Utilisant une niethode combinant la chromatographie en phase gazeuse et la calorimetric, on a mesure les chaleurs de vaporisation des hydrocarbures suivants: niCthyl-1 cyclopentene, methyl-3 cyclopentene, ethylidenecyclopentane, ethyl-1 cyclopentene, mCthyltnecyclohexane, allylcyclopentane, vinylcyclohexane, tthylidenecyclohexane, allylcyclohexane, diethyl-3,3 pentane, tetramethyl-2,2,4,4 pentane et tttramtthyl-2,2,5,5 hexene-3 trnns. On a combine ces valeurs avec les chaleurs deformation de ces liquides qui avaient Ctt rapporttes anterieurement afin d'en tirer les valeurs de AH, en phase gazeuse. Les resultats indiquent que les doubles liaisons internes sont favorisees par environ 0.5 kcal/mol par rapport aux doubles liaisons exo dans les cycles a 5 et a 6 chainons; toutefois la difference entre ettdo et exo est beaucoup plus faible que ce qu'on croyait anterieurement. En se basant sur les schkmas d'additivite des groupes, il aurait ete impossible de predire adtquatement plusieurs des capacites calorifiques mesurkes.[Traduit par le journal]A much discussed conceDt more than two decades ago was the idea that the internal (endocyclic) double bond is thermodynamically favored over the exocyclic double bond in six-membered ring systems, whereas the reverse was believed to be true in fivemembered rings (1). However, Turner and Garner (2) measured the heat of hydrogenation (acetic acid solution, 25°C) of 1-methylcyclohexene, methylenecyclohexane, 1-methylcyclopentene, and methylenecyclopentane, and found that hydrogenation of the exo double bond is more exothermic in both the five-membered ring (by 3.7 kcal/mol) and sixmembered ring (2

Structural and Energetics Studies of Tri- and Tetra-tert-butylmethane

“…Referring to the thermochemical data reported in Table , it is seen that the G3 and G3(MP2) Δ H f298 values of di-TBM are −245.2 and −243.9 kJ mol -1 , respectively, using eq 1 of the atomization scheme. These two values are in excellent agreement with the experimental result, −241.5 ± 1.5 kJ mol -1 . The corresponding Δ H f298 values of di-TBM with the isodesmic scheme are −248.3 and −247.6 kJ mol -1 , also in very good agreement with experiment.…”

Heats of Formation of Medium-Sized Organic Compounds from Contemporary Electronic Structure Methods

“…Second, only small organic and inorganic molecules for which accurate formation enthalpies are known have been used to equilibrate the reactions (i.e., were used as A, B, and D in eq ), in particular acetylene, ethylene, ethane, CO, methane, H 2 , H 2 O, H 2 S, HCN, N 2 , and NH 3 . We expect under these conditions that the possible cancellations of errors are minimal, and better insights into the ability of the electronic structure theory methods to provide accurate reaction enthalpies can be gained. …”

Thermodynamic, energetic, and topological properties of crystal packing of pyrazolo[1,5-a]pyrimidines governed by weak electrostatic intermolecular interactions

“…In this work, gas chromatography was used to measure the vaporization enthalpy (ΔH vap (298 K)) in accordance with the method that was proposed by Peacock and Fuchs [20][21][22][23][24][25] . and modified by Chickos et al [26][27][28] The pyrazoloij1,5-a]pyrimidines 1, 5, 6, 7, 9, 12, and 13 were chosen for this study and there were at least two compounds in each of the groups formed according to the substituent in R 7 : compounds 1 and 13 with R 7 = CCl 3 ; compounds 5, 6, and 7 with R 7 = CF 3 ; and compounds 9 and 12 with R 7 = aryl/heteroaryl.…”