5448
COMMUNICATIONS TO THE EDITOR
cases, the formation of the cyclopropane ring is stereochemically specific, resulting exclusively from cis addition. Mechanistically the addition appears t o occur in a single step withc-t rotating intermediates. &Butene is the only olefin found so far with which methylene reacts with discrimination. A possible explanation involving dipolar association prior to absorption of light and decomposition is being investigated. We acknowledge with thanks the support of a grant by the Research Corporation. STERLING CHEMISTRY LABORATORY [ALE UNIVERSITY VON E. DOERING NEWHAVEN,CONN. P . LAFLAMME RECEIVED AUGUST15, 1956
w.
Vol. 78
68’; IVDA: liquid) which all have cyclopropane structures (e.g., IDA).^ Pyrolyses a t 200-300” fur-
,
CH O O C L LH
;qL
+
~i7-CoocH,
COOCH, IDA
RY b ‘
VI
t
D - C O O C H ,
COOCH,
VI1
nish dimethyl phthalate, trimethyl benzene-1,2,3tricarboxylate, trimethyl benzene-1,2,4-tricarboxylate and dimethyl phthalate, respectively : conTHE STRUCTURE OF THE BUCHNER ACIDS firming structure I for “norcaradienecarboxylic Sir: acid,” establishing structures I1 and I11 for a- and To norcaradienecarboxylic acid (I, liquid), cy- @-acidsand being inconclusive about y-acid. In the aliphatic C-H region (displaced 27-30 (11, m.p. 71.5”), @-(III,m.p. 59.5’), y- (IV, m.p. 64.5’; amide, m.p. 85’) and the 8- (V, m.p. 31’) milligauss [benzene 0.01, Varian Associates Nucycloheptatrienecarboxylic acids, the five CsHsOz clear Magnetic Resonance Spectrometer, 30 megaacids uncovered in the laboratories of Buchner and cycles, 7047 gauss field strength) the NMR specEinhorn (see Grundmann and Ottmann’ for refer- trum of 1~~shows one hydrogen atom split into a ences), Buchner tentatively assigned structures Ib, triplet by coupling with two equivalent, adjacent I V C , ~IIc, IIIc and IC, respectively; DeJong,a hydrogen atoms (in complete accord with structure structures Ib, IVc, IIIc, ICand IIc; and Grund- I) ; I I M e and IIIM,show two hydrogen atoms, likemann and Ottmann,’ structures Ib, IC, IIIc, IVc wise split into triplets (in accord with the assigned structures) ; IVMe also shows two hydrogen atoms, which being split into a doublet, unequivocally implies coupling with one adjacent hydrogen atom. Consequently only structure IV is tenable Ia for y-acid. The NMR spectra of the four methyl esters and COOH of tropilidene are so similar and so uniquely complicated in the vinyl C-H region that one valencytautomeric system2must be common to all. In an important application of NMR, Corey, Burke and Ib Remers6 have excluded type b (norcaradiene) as the structure for tropilidene. Similarly, none of the Buchner esters may have a type b structure. 1,3,5-Cyclooctatriene which necessarily has a non-planar, type c structure has only one simple IC NMR absorption in the vinyl C-H region and a resonance energy of 2 kcaLs By contrast troCOOH ‘horcaradienepilidene has an exceptionally complicated NMR carboxylic a c i d “ spectrum and a resonance energy of 6-8 kcaL6 It and IIc. We wish to communicate evidence by therefore seems highly probable that tropilidene which the “8-acid” is removed and structures Ia, and the Buchner acids have the planar, pseudoIIa, IIIa and IVa are assigned to the four remain- aromatic type a (tropilidene) structure. ing acids. HICKRILL CHEMICAL W. VON E. PORRING Since V and a 47:53 mixture (m.p. 31’) of I1 and RESEARCH FOUNDATION G. LABER N. Y. R. VONDERWAHL I11 have superimposable infrared spectra and since KATONAH, HUMBLEOILAND REFINING Co. N. F. CHAMBEBLAIN a-amide (m.p. 127”) can be crystallized from ‘‘8- BAYTOWN, TEXAS R. B. WILLIAMS amide”, “8-acid” is non-existent. RECEIVED SEPTEMBER 17, 1956 The methyl esters (IMe, I I M e , I I I M e and IvMe) Of the four remaining acids react with dimethyl acetylenedicarboxylate to give infrared-spectroscopically (4) K . Alder and G . Jacobs, Bcr., 1528 (19531, demonstrated this different, non-intercontaminated Diels-Alder ad- type of structure for the tropilidenemaleic anhydride adduct. In addition to VI, pyrolysis of IDA gives VI1 (hydrogenated and saponiducts (IDA: m.p. 76’; IIDA: liquid; 1 1 1 ~ m.p. ~: fied to cyclopropanecarboxylic acid and being investigated as a source (1) Ch.Grundmann and G. Ottmann,Ann.. 683, 163 (1953). (2) Three possible sets of valence tautomeric structures, illustrated by Ia, I b end IC,are designated by a, band c. (3) A. W.K . DeJong, Rcc. trow. chim., 66, 198 (1937).
of CaHa +). Hexahydro IIDAand IIIDAshow C-CHI. (5) E. J. Corey, € J. I. Burke and W. A. Remers, THISJOURNAL, 77, 4941 (1968). (6) Professor R. B. Turner, private communication.
