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The geometrically isomeric cis-and trans-3-methyl-4-ethyl-3-carbomethoxy-A~-pyrazolines were prepared and their pyrolysis and photolysis studied. The isomeric pyrazoli~les gave cyclopropane products of mixed stereochemistry, but predominantly with retention of the stereochemistry present in the starting pyrazoline. Each pyrazoline gave stereospecifically a different a,p-unsaturated ester product. This stereospecificity can be related to the structure of the pyrazoline through the requirement that the loss of nitrogen must be from the side of the pyrazoline that is trans to the hydrogen at C-4.

cis-and tra~zs-3,5-Dimethyl-3-carbo11~ethoxy-A~-pyraoline (IV and V) have been separated, and , . product analysis for the pyrolysis and photolysis of these compounds has been completed.I he cyclopropane products are formed with some change in the relative coniig~iration of the cis-trans groups in both reactions. 'The a,@-unsaturated olefir1 prod~rct is formed stereospecifically with IV, yielding methyl 2-methyl-cis-2-pentelloate (XI), and with V, yielding methyl 2-methyl-tra?zs-2-pentenoate 0 ; ) . The results of the pyrolysis and photolysis of cis,tra?ts-3,4,5-trimethyl-3-carbornethoxy-A1-pyrazoline are also described. T h e product s t~~d i e s and some kinetic s t~~d i e s are the basis of a new ~nechanisrn proposed for the pyrolysis of pyrazolines.Recent studies on the pyrolysis of pyrazolines have reopened the question regarding the stereocheinistry of the conversion of pyrazolines into cyclopropanes (1-3). This reactio~l was reported by von Auwers (4) to be essentially stereospecific and this was the accepted view on the reaction for many years (stereospecific here is used t o mean t h a t the substituents on the cyclopropane ring have the same cis-trans relationship as on the initial pyrazoline). \Ian Aulcen and Rinehart (1) showed that the pyrolysis of a pair of isomeric pyrazolines with inethyls cis and trans on Cg and Cq (c0111pounds I and 11) gave cyclopropanes with effective randoinization of this cis-trans relationship. On the other hand, Overberger and Anseline (2) have found that the pyrolysis of trans-3,5-diphenyl-a'-pyrazoline (111) gave stereospecifically the trans-1,2-diphenyl~~rclopropane, and thus the stereocheinistry of this reaction is not clear.\lie have prepared some new pyrazolines, \vhich shoxv a cis-trans relationship a t positions Cs and Cj, in an effort to find out more about the pyrolysis reaction. T h e preparation of a cis-trans mixture of 3,s-dimethyl-3-carboinethoxy-A1-pyrazoline and its pyrolysis was reported earlier ( 5 ) . This mixture has now been separated by distillation through a spinning-band coluilln a t a temperature slightly below the pyrolysis temperature. T h e lower-boiling isoiner has been assigned the structure with the methyl groups cis (I\/) and the higher-boiling isoiner t h a t ~v i t h the methj.1 groups trans (V). T h e preparation and ex m, x = c o , c~, 11, X = COCH, N +

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The results of analysis of methyl citraconate and mesaconate, methyl cis-and transcrotonate, and methyl cis-and trans-2-petitenoate are reported. A previously reported analysis of the crotonates by first-order perturbation theory gave significantly dilferent values for the 1,3 coupling constants. The discrepancy in results, which is due to the i~nportance of secondorder effects, emphasizes the need for caution in applying the first-orcler neth hod. From values of 1,3 coupling constants reported here and elsewhere it is concluded that there is no simple relation between the magnitude of 1,3 coupling constants and geometrical configuration of the interacting nuclei.Much attention has been devoted recently to the N.M.R. spectra of substituted propenes and butenes (1-7). Two aspects of the spectra have received special attention. The first is the magnitude of the 1,3 coupling constants." Whipple et al. have reported 1,3 coupling to be consistently greater in the trans 2-substituted propenes (J1,3 than in the cis isomers (2) (J1,3 trans). In tiglic and angelic acids and their nlethyl esters the opposite was found (1). Subsequently Jackinan and Wiley (4) provided evidence which gave a different assignment to the protons of a-methacrolein from that of Whipple et al. and thus provided another case where J I ,~ trnns was greater than J I ,~ cis. T h e second aspect was the basis of Jackman's studies. He presented compellillg evidence for the use of chemical shifts to assign configuration to a-P unsaturated esters. Among the compounds which he has studied were the methyl esters of mesaconic, citraconic, and cisand trans-crotonic acids. We have examined these same four esters in addition to the methyl esters of cis-and trans-2-pentenoic acid. The more exact method of analysis employed in our case has provided some results of particular interest in this field. Methyl Mesaconate and Methyl Citraco7zateT h e olefinic and C-methyl protons in these esters comprise an AX3 system. Analysis of such a system can be made by first-order perturbation theory. T h e complete results are listed in Table I. All coupling constants in this paper are reported with a n estimated accuracy of f 0.05 cycle/sec as the standard deviation of each lneasurement was e 0 . 0 5 cycle/sec. The coupling constants in Table I