The rs structure of trans-acrolein has been determined from the microwave spectra of eleven isotopic species: CH2=CH–CHO, 13CH2=CH–CHO, CH2=13CH–CHO, CH2=CH–13CHO, CH2=CH–CH18O, CHD=CH–CHO, CDH=CH–CHO, CH2=CD=CHO, CH2=CH–CDO, CHD=CD-CHO, and CDH-CD-CHO. In the structural parameters listed below the subscripts t and c on the H atoms of the CH2 group designate the trans and cis positions, respectively, with respect to the aldehyde group. rs(CHt) = 1.086±0.005, rs(CHc) = 1.086±0.005, rs(CH) = 1.084±0.003, rs(CHald) = 1.108±0.003, rs(C=C) = 1.345±0.003, rs(C–C) = 1.470±0.003, rs(C=O) = 1.219±0.005 Å, ≰CCHt = 121°27′±10′, ≰CCHc = 119°58′±10′, ≰C=CH = 122°50′±10′, ≰CCC = 119°50′±10′, ≰CCHald = 115°6′±10′, ≰CCO = 123°16′±20′. For the normal species, transitions were observed in torsional vibrational levels up to v = 9, but no spectrum was observed for the cis (or gauche) conformer.
Various methods have been used, including the chromatographic analysis of non-gaseous products and free radical detection with ferric chloride, to investigate the mechanism of the gOSr----!JOY beta-radiolysis of liquid benzene. The initial G for reduction of FeCl3 is strongly dependent on [FeCI3] and may be as high as 10; it falls rapidly with increasing dose to a constant value of 0866012. It is concluded that the most important primary act leads to the formation of phenyl radicals and hydrogen atoms, together with electronically excited benzene molecules of two types, one with a lifetime of -100 psec tentatively assigned to the 3Blu state and the other, of shorter life, which may be the lBzu state. The C6H5 radicals and H atoms are very reactive towards benzene, and FeC13 scavenges only secondary, less reactive, radicals but can also be decomposed by interaction with a benzene molecule in either state of excitation.Whereas hydrogen and acetylene are the only gaseous products in the radiolysis of liquid, air-free benzene,l-3 the non-gaseous products, often termed " polymer", have been only partially characterized. Gordon, van Dyken and Doumani 3 have shown that the " polymer ", obtained from the W o -y irradiation of benzene, contains a Clz fraction which constitutes 18.8 % w/w of total "polymer", a C18 fraction (57.6 %) and a >CIS fraction (23.6 %). Although biphenyl was the only C12 product positively identified 3 (cf. ref. (4)), four other members of the Cl2 group have been distinguished 5 ; two were positively identified as phenyl cyclohexadiene-2,4 and phenyl cyclohexadiene-2,5, a third is probably phenyl hexatriene and the fourth was not identified. The identity of the c 1 8 and > C18 products is even less certain. There appear to be a large number of CIS products 5 and this fraction may contain " hydrogenated terphenyls and terphenyls ". 3 Values of G(H2), G(C2H2), G(diphenyl), and G(benzene+" polymer "), obtained by several workers, are presented in table 1.
Surface catalyzed isomerization of (CH,),O to CH3CH0 occurs in a small, Pyrex reactor containing 15 or 230 Torr (CH,),O at temperatures in the range 339.2 "C to 461.4 "C. Ro(CH3CHO), the initial rate of formation of CH3CH0, depends on the number of successive pyrolyses and on the evacuation time between pyrolyses, which is not true of the initial rates of formation of Hz, CO, CH,, CH,CO, and C2H6. Ro(CH3CHO) also depends on the reactor S / V and on pretreatment of the reactor with product gases, particularly H,. The reproducible and limiting values of Ro(CH3CHO) are independent of the (CH,),O pressures used. Above 385 "C these initial rates exhibit an Arrhenius temperature dependence while below 385 "C they pass through a maximum.Analysis of the Langmuir-Hinshelwood, low surface coverage mechanism shows that the T > 385 "C isomerization is partially or totally controlled by C H 3 C H 0 desorption and that -AH:,,;,,, < (55 i 10)kcal mol-I, for CH,CHO on this surface. E, = 57 kcal mol-I for the homogeneous first order deconlposition of (CH,),O, in the 15 Torr pyrolysis at temperatures in the range 374.0 to 406.7 "C, and any vibrationally excited CH,CHO, formed in the gas phase at this pressure (and possibly even at 230 Torr), dissociates into chain initiating radicals. L'analyse du recouvrenlent faible de la surface selon Langmuir et Hinshelwood ~nontre que I'isomCrisation pour T > 385 "C est partielle~nent ou totalenlent contr61Ce par la dksorption de CH,CHO et que -AH.,,, < (55 i 10) kcal mol-' pour CH3CH0 sur cette surface.La d6composition honiogene du premier ordre de (CH2),0 a un E:, = 57 kcal mol-I dans la pyrolyse sous 15 Torr et a des temperatures de 374.0 a 406.7 "C; le n~ethanal formC en phase gazeuse et vibration-
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