type strain was demonstrated directly from the nuclear magnetic resonance studies of the acyl and nitroso derivatives of 2-methylpiperidine (2 series) and 2,6-cis-dimethylpiperidine (1 series). In these two series, the bulky 2-methyl groups are forced to assume the axial conformation due to a severe A('s3) interaction in the equatorial conformation. The free energy of activation (AG*) for the internal rotation around the N-C and N-N bonds in la-lg was determined. The comparison of these AG* values with those of the corresponding derivatives of dimethylamine indicates the decreases are in the range of 3.64.7 kcal/rnole which is in fair agreement with the conformational energy of 1,3-diaxial CH3/CH3 interaction. An argument was presented to show that this interaction energy corresponds t o the decrease of AG* in l a -l g .C a n a d~a n Journal of Chemistry, 46, 2821Chemistry, 46, (1968 The stereochemical coilsequence of reactions parently represent quantitatively the extent of of 2-alkylcyclohexane derivatives (A S B) has the delocalization energy and also qualitatively led Johnson to conclude that there is a severe the extent of the planar configuration a t N=C non-bonded interaction between the group X 0 (or X') and an equatorial alkyl group (1). This and N=N bonds in 1 and 2 (where -C // interaction was termed A(''3) strain (1) and the \ D energy was approximated with 1,3-diaxial CH3/ CH, interaction (3.7 kcal/mole). During our studies on the photochemical behavior of nitrosamines we became aware of some unusual reactivities (2) and nuclear magnetic resonance (n.m.r.) characteristics of N-nitroso-cis-2,6-dimethylpiperidine (lg, N-NO for NCOR) that might be related to A('.,) strain. The n.m.r. study on the conformational aspects of the acyi derivatives of cis-2,6-dimethylpiperidine (1 series) and of 2-methylpiperidine (2 series) was undertaken. The purpose of this communication is to demonstrate directly the presence of the A(133) interaction by n.m.r. spectroscopy in systems 1 and 2 and further to provide a method of estimating the conformational energy of 1,3-diaxial CH,/CH, interaction in 1. . ; i systems due to an extensive delocali-(N=N ) zation of the lone pair electrons of nitrogen with the hetero n electron system has been well documented by n.m.r. spectroscopy (3, 4). The rotational barriers due to the partial double bond character (15-21 kcal/mole for amide and 23.3 kcal/mole for dimethyl nitrosamine) apn is either acyl or nitroso group). The structure of these acyl derivatives, if the A('v3) interaction is ignored for a moment, must be represented by the nearly trigonal configuration at N as in 1 and 1'. With a planar or a near planar structure at the N=C bond, it is expected, and can be shown by Dreiding Models, that A('z3) interaction between 0 (and/or R) and a-equatorial CH, is severe in 1' and that 1 is the predominant conformation. Since the delocalization energy (15 N 23 kcal/mole) is several times higher than the 1,3-diaxial CH,/CH, interaction, the amount of conformer 1' will be negligibly s...

It has been established that alkylnitrosamines undergo photoreduction in methanol solutions in the presence of an acid to give the parent amine, formaldehyde, and N-aminoformamide. Where it is possible, an exchange reaction between theS-hydrogen and the nitroso group isalso observed during this photolysis. However, photoelimination also occurs in competition with photoreduction, the extent of which is dependent on the rates of the two photoprocesses. In aqueous solutions, N-nitrosamines predominantly undergo photoelimination. Those nitrosamines that undergo rapid photoelimination or photoreduction d o not efficiently add to olefins photolytically. Conversely if photoaddition is retarded, a nitrosamine takes elimination or reduction pathways. Excitation of n + X* or x + X* transition band of N-nitrosamines gives virtually the same photoreaction patterns. Minor differences in the photoproducts are attributed to other secondary reactions.I1 a t t t ttabli que les alkylnitrosamines sont photortduites dans des solutions de mtthanol en presence d'un acide pour donner l'amine apparentte, du formaldthyde et du N-aminoformamide. Lorsque c'est possible, on observe aussi une reaction d'tchange entre I'hydrogtne-6 et le groupe nitroso durant cette photolyse. Toutefois, la phototlimination arrive aussi en compttition avec la photortduction, dont I'importance depend des vitesses des deux proctdts photolytiques. En solutions aqueuses, les N-nitrosamines subissent la phototlimination de f a~o n prtdominante. Ces nitrosamines qui subissent une photortduction ou une phototlimination rapide ne s'additionnent pas photolytiquement aux oltfines de f a~o n efficace. D'autre part, si la photoaddition est retardte, une nitrosamine entreprend un mtcanisme d'tlimination ou de rtduction. L'excitation de la bande de transition n -t A* ou A + A* des nitrosamines donne virtuellement les m&mes modtles de photortaction. Des differences mineures dans les photoproduits sont attributes a d'autres rtactions secondaires.

. Can. J. Chem. 54, 3517 (1976).The acyclic amido radicals generated from the corresponding N-bromo.AT-iert-alkylamides reacted like ,?'-radicals, rather than 0-radicals, and preferentially abstracted a 6-hydrogen of the alkyl chain, rather than a r-iiydrogen of the acyl chain. On the basis that, in these amido radicals, the conforn~ation of the transition state of the hydrogen transfer is a five-membered ring and the stereoelectronic requiren~ent for the transfer demands a colinear arrangement of the radical containing orbital and the C-PI bond, the results are satisfactorily rationalized by the n electron configuration of the amido radicals. It is also established that the chain length of these N-bromoamide photodecompositions increases as the intran~olecular hydrogen transfer of the corresponding amido radicals becomes easier; the hydrogen abstraction step must be the rate determining step in the chain reaction. The spontaneous formations of r-iminolactones from r-bromoamides indicate that the intramolecular nucleopliilic displacement by the 0-center of the amido group is facilitated since its transition state conformation readily accommodates the stereoelectronic requirements for the nucleophilic substitution. A colinear approach of thep-orbital of the more nucleophilic N-center to the rear side of the yC-Br bond is shown to be prohibitively strained. Chem. 54, 3517 (1976).Les radicaux amido acycliques, gknCrCs B partir des N-bromo N-tert alkylamides correspondantes, reagissent comrne les radicaux N-alkyles plutBt que comme des radicaux 0-alkyles; ils rkagissent prCf6rentiellement pour enlever un hydrogkne en 6 de la chaine aIkylCe plut6t qu'un hydrogkne en 7 de la chaine acylCe. En faisant l'hypothbse que, dans ces radicaux amido, la conformation de 1'Ctat de transition du transfert d'hydrogene est un cycle a cinq membres et que les conditioils stCrCoClectroniques pour le trarsfert demandent un arrangement colinCaire de l'orbitale contenant le radical et du lien C-H, on peut rationaliser d'une fason satisfaisante les resultats par la configuration Clectronique IT des radicaux amido. On a aussi Ctabli que la longueur de la chaine de ces photodkcompositions de N-bromoamides augmente B mesure que le rransfert d'hydrogbne intramolCculaire des radicaux arnido correspondants devient plus facile; I'6tape de l'enlkvement de l'hydrogene doit &tre l'ktape dCterminante dans la reaction en chaine.Les reactions spoi~tanCes de formation de r-iminolactones B partir de r-bromoan~ides indiquent que le dkplacement nuclCophile intramolCculaire par l'intermediaire du centre oxygCnC du groupe amido est facilite puisque la conformation de son Ctat de transition accommode facilement les demandes stCrCoClectrorliques de la substitution nuclCopbile. La tension provoquCe par une approche colineaire de l'orbitale p du centre azote, qui est plus nuclkophile, vers la face arrikre du lien -y-C-Br est prohibitive.[Traduit par le journal]In recent. years, the existence of anlido radi-(81, and reaction patterns (9-13). These results cal...

Novel oxidations attending the photorearrangement of a nitrosamide and the photoaddition of nitrosamine are described and compared with the corresponding non-oxidative photoreactions.hWith proper filters, disproportionation during photorearrangement of N-nitrosohexylacetamide and tautomerization during nitrosopiperidine photoaddition to cyclohexene can be minimized togive improved yields of the antidimers of C-nitroso compounds. These side reactions are shown to be exclusively derived from secondary photoreactions of the C-nitroso compounds. In the presence of oxygen. the courses of the photoreactions are diverted cleanly to form nitrate esters. Oxygen reacts with nitric oxide, both in the free state and when paired with the C-radical thus diverting the course of the reaction. The rate constant of radical combination between a C-radical and nitric oxide is estimated to be in the range of 2 x lo7 s-l.De nouvelles oxydations accompagnant le photortarrangement de la nitrosamide et la photoaddition de la nitrosamine sont decrites et comparkes avec les photoreactions non-oxydantes correspondantes. Avec des filtres convenables, la dismutation durant le photorearrangement de la N-nitrosohexylacCtamide et la tautomerisation durant la photoaddition de la nitrosopiperidine au cyclohextne peuvent &tre reduites au minimum pourainsi donnerde meilleurs rendementsen dimeres-co~ti des composCsC-nitroso. Ces reactions parasites proviennent, tel qu'il a tte demontre, exclusivement de photoreactions secondaires descornposes C-nitroso. En presence d'oxygene, le cheminement des photorkactions est netternent rnodifii pour former des esters nitrate. L'oxygene reagit avec l'oxyde nitrique, a la fois a I'etat libreet lorsque pairk au C-radical, pour ainsi dCvier le chemin de la reaction. La constante de vitesse de la combinaison radicalaire entre le C-radical et I'oxyde nitrique semble se situer dans les alentours de 2 x lo7 s-I.[Traduit par le journa]] Can.

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