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Pyrolyscs of toluene, ethylbenzene, propylbenzene, and b u tylbeuzene have given the compounds listed in thc Table . The yields of higher p l ycyclic hydrocarbons varied with the nature of the aliphatic side chain, arid mechanisms of formation based on scission of molecules to radical intermediates and re-synthesis are proposcd. The highest yields of the carcinogenic hydrocarbons 3,4-benzopyrene and 3,4-benzofluoranthene were obtained from butylbenzene.

79.5 74.5 Z-Gly-L-Ala L-Phe-OMe <3 5 10 12 78.0 71 .O Z-Gly-L-Phe L-Ala-OMe <3 9 17 17 7 7 . 5 7 0 . 5 Z-Gly-Gly-L-Phe L-Ala-OMe 10 15 25 20 81.5 72.0 For-L-Phe L-Ala-OMe <3 <3 <3 <3 7 9 . 5 72.5 Ac-L-Ala L-Phe-OMe <3 <3 35 27 79.0 7 1 . 5 a For = formyl; all other abbreviated designations of compounds follow IUPAC-IUB rules. * The optical purity of the starting materialswas verified by gas-liquid partition chromatography : N-acetyl and N-benzoyl compounds were converted to the menthyl ester derivatives, while the N-formyl compounds were hydrolyzed and analyzed as the N-trifluoroacetyl-L-prolyl peptide esters; the methyl ester compounds were assayed similarly.' c The limit of measurement was generally 3 z, although in some cases a more accurate value was obtained by duplicate procedures. All spectra were determined on a Varian A-60 spectrometer with the center of gravity of the chemical shift given in hertz downfield from tetramethylsilane ( J = 7.2 i 0.3 Hz). The compounds were dissolved in deuteriochloroform (deuterioethanol for the tetrapeptide).nuclear magnetic resonance (nmr) spectra.14* The methyl doublet signal in an L-L (or D-D) compound was at lower field than the equivalent signal for the D-L (or L-D) analog due to deshielding and offered a potentially convenient means for the quantitative analysis of such mixtures. We have now employed this technique to examine the influence of several coupling agents and N-acyl protecting groups on the extent of racemization during peptide synthesis.In a typical experiment, N-acetyl-L-phenylalanine (0.207 g, 1 mmole), carbonyldiimidazole (0.162 g, 1 mmole), and methylene chloride or acetonitrile (5 ml) was stirred at -5" for 1 hr. The hydrochloride of L-alanine methyl ester (0.139 g, 1 mmole) and triethylamine (0.14 ml, 1 mmole) were added and the solution was kept at 0" for 15 hr. After suitable washings, the solution was dried and evaporated; the solid residue was redissolved in deuteriochloroform and the solution was used for nmr analysis.

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Three acylating mechanisms are involved in the reaction between amides and anhydrides. In the aliphatic series all mechanisms are governed by the indilctive effects operating in the reactants.Amides act as acids towards anhydrides. Diacylimines and the corresponding anhydrides acylate alcohols by the same mechanism.A new compound, propionylchloroacetarnide, has been prepared. Properties of some diacylimines have been established. Uses for diacylimines are suggested.

l9F n.m.r. studies of the inclusion of 0-, m-, p -and a-fluoro-trans-cinnamates and 0, p -and a,p-difluoro-trans-cinnamates by a-cyclodextrin (aCD) have shown that two inclusion equilibria K1 S + aCD e S.aCD K P S * aCD + aCD s S -(aCD), are established in D,O solution at pD = 8.5 & 0.1. Typically at 294 K, Kl = 1 1 1 & 13 dm3 mol-' and K, = 23 2 dm3 mol-1 for a,p-difluoro-trans-cinnamate. Chemical-shift and other data indicate that the predominant S . aCD complex is that in which the carboxylate group of the fluorocinnamate enters the wide end of the aCD cavity, delineated by twelve secondary hydroxy groups, first. The S . (aCD), complex probably has a structure in which the fluoro-trans-cinnamate is encapsulated by two aCD with the wide ends of their cavities in close proximity. a-Cyclodextrin (aCD) or cyclohexa-amylose is a six-membered a-1,4-1inked cyclic oligomer of D-glucopyranose [structure (I)], which forms inclusion complexes with a variety of substrates in aqueous so1ution.1-6 Usually the 1 : 1 complex S -aCD is readily formed and a 1 : 2 complex, S.(aCD),, has also been observed although there have been few studies of this latter specie^.^.^ A knowledge of the stoichiometry of the cyclodextrin inclusion complexes and the environmental changes experienced by the substrate on inclusion is of intrinsic interest. This interest is increased by the use of cyclodextrin inclusion complexes as models for the host-guest interaction thought to be important in enzyme-substrate and drug-receptor systems, and also by the potential importance of cyclodextrin inclusion complexes in the design of controlled chemical syntheses. 1-6 lH and 13C n.m.r. spectroscopy has proved to be a powerful tool in the study of cyclodextrin inclusion complexes7~ 9 , lo but has been hampered by the substantial number of resonances arising from both the cyclodextrin and the included substrates. The use of selectively fluorinated substrates and 19F n.m.r. spectroscopy avoids such potential difficulties and has provided considerable insight into enzyme-substrate interactions.11-16 Accordingly in this study 19F n.m.r. spectroscopy is employed to 3147