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The overall photochemical transformations of 3-alkyl-6,6,9,9-tetramethyldat5( lO)-hexalins have been determined. In addition, the relative quantum yields of disappearance of the diene and the relative rates of reaction of the related trienes have been determined. By evaluation of all these data, it was established that the photostationary state between diene and triene was controlled by the conformation of the triene. A triene with a preferred s-cis,s-cis conformation is less favored in the photostationary state than a triene with an s-cis,s-trans conformation, The preferred conformation of the triene was determined by the steric size of the 3-alkyl group of the original diene. It was also shown that a triene with an s-cis,s-cis conformation was transformed to a vinylcyclobutene whereas a triene with an s-cis,s-trans conformation was transformed to a bicyclo[3.1.0]hexene. Part AThe 1,3-cyclohexadiene chromophore, one of the first groupings studied photochemically in detail due to its role in the in vivo formation of vitamin D,4a is the starting point for a wide variety of photochemical reactions. Many types of compounds containing this grouping have been studied4b and a general summary of the results obtained is given in eq 1. To date, no single compound has been reported to exhibit all these reactions and 1,3-cyclohexadiene is used in eq 1 simply as -an example.In this overall photochemical reaction scheme there are both reversible and irreversible processes. In general, the quantum yields for the reversible processes, at the wavelength of light employed (A >220 nm), are higher than those for the irreversible reactions and, thus, at the early stages of the photochemical process a temporary photostationary state between the 1,3-cyclohexadiene and the 1,3,5-hexatriene is found. The composition of this photostationary state is dependent upon the substitution pattern of the diene system. For ex-

Rksumd. En faisant reagir des acides aminis en solution aqueuse, B temperature ordinaire et i pH env. 11, en presence de polyphosphates cycliques ou linkaires, on obtient des dipeptides avec des rendements allant jusqu'a 40%. Dans le cas de la sirine, on note uniquement la formation du derive 0-phosphoryle, soit l'acide sCrinephosphorique.En faisant reagir un melange de glycine (ou d'alanine) et de l'une des trois amines suivantes: phosphosdrine, phospho6thanolamine ou acide amino-2-ithanephosphonique, en solution aqueuse en presence de trimetaphosphate, on obtient B cat6 de la diglycine des quantites apprkciahles d'amide mixte, soit la N-glycyl-phosphoserine, la N-glycyl-phosphoethanolamine et l'acide Nglycyl-amino-2-Bthanephosphonique respectivement. Nous pensons que des peptides, phosphopeptides et amides mixtes de ce type sont Cgalement form& lors de reactions par decharge Blectrique dans des systkmes contenant de la phosphine, du methane, de l'ammoniac et de l'eau.Un mecanisme probable conduisant a la liaison peptidique ou amide serait la formation intermediare d'un acylphosphate cyclique ou ouvert de l'acide amink, qui rkagirait ensuite avec le groupe amino d'une deuxikme molecule d'acide a m i d (+ peptide) ou de l'amine (+ amide).Ces reactions prdsenteraient un certain interst dans la formation prCbiotique de la liaison peptidique et amide, ainsi que de la liaison ester phosphorique.We have reported that several amino acids are condensed to dip-ptides in aqueous solutions of cyclic or linear polyphosphates, at pH above 7, at 70" and room temperature [l]. In the case of cyclic polyphosphates the best yields are obtained with trimetaphosphate, while for linear polyphosphates the yields increase with their average chain lengths. When hydroxy amino acids like serine are used, the main product from the reaction is 0-phosphoserine, and only very small amounts of peptide are formed [l].We have also previously found that when electric discharges are passed through mixtures containing phosphine'), methane, ammonia, and water (believeci to be l)The possibility of existence of phosphine on the primitive earth has already been discussed [Z].