Hans Cerfontain

Conformational study on some β-phenyl-α,β-unsaturated ketones

Abstract The conformation of three (E)-β-phenyl-α,β-unsaturated ketones and their corresponding (Z)-isomers 1, 2, and 3 was established by IR and ASIS. (Z)-1 and (E)-1 have exclusively the s-trans conformation. The two isomers of 2 occur in both conformations but there is a higher s-cis to s -trans ratio with the (Z) than with the (E)-isomer. (Z)-3 appears to exist exclusively in the s-cis conformation, the (E)-isomer has a small content of the s-trans conformation. It was concluded that the ASIS for Hb, is a measure of the s-cis content of the conformational equilibrium.

Aromatic sulphonation with sulphur trioxide in trichlorofluoromethane as a solvent

Abstract The sulphonation of p-dichlorobenzene with sulphur trioxide has been studied in trichlorofluoromethane as solvent. The main products are (pyro)sulphonic acid and sulphonic anhydride. The formation of sulphone is very small. The sulphonation is of first order with respect to both substrate and sulphur trioxide, and proceeds without a primary kinetic isotope effect of hydrogen (kH/kD = 1·08 ± at −28°). The mole-ratio of consumed sulphur trioxide to converted p-dichlorobenzene is equal to 2. It is suggested that the sulphonation proceeds via 1-benzenonium-1-sulphonate and 1-benzenonium-1-pyrosulphonate as the subsequent reactive intermediates, the formation of the former intermediate being rate limiting. The dependence of the sulphonation products on reaction time indicates that the (pyro)sulphonic acid is the initial product and that the sulphonic anhydride is formed at a later stage. The experimental data accord with formation of the anhydride by reaction of the pyrosulphonic acid with 1-benzenonium-1-sulphonate. The kinetics of sulphone formation comply with a mechanism in which ArS3O9 is the effective sulphonylating entity.

Sulfonation of alkenes with sulfur trioxide. Stereospecific β-sultone formation

Abstract Sulfonation of 1-octene, ( E )-1-deuterio-1-octene, and ( Z )- and ( E )-4-octene with one mol-equiv of sulfur trioxide yields the β-sultones 2a - d respectively. The reaction proceeds stereospecifically via a concerted cis -cycloaddition.

Photochemistry of dienones-VIII: The low temperature photochemistry of (z)-β-ionone and its photo-isomers

Abstract The isomerizations of (E)-β-ionone 1, and of mixtures of the isomeric pyran 2 and (Z)-β-ionone 3 in CD3OD as solvent on direct irradiation with λ 254 nm and on triplet photo-sensitization have been studied at temperatures ⩽ - 50°, where the thermal isomerization between 2 and 3 is fully inhibited. The direct irradiation of 1 at -60° leads to 3 and (Z)-retro-γ-ionone 4 as primary products; 3 is subsequently rapidly photo-converted into mainly 2. Evidence is presented that 4 is also a primary photoproduct from both 2 and 3. The quantum yield ratio φ2→4:φ3→4 ⋍0.50. On starting with either 1 or mixtures of 2 and 3 the same photo-stationary equilibrium ratio of 1-3 is eventually obtained, viz 1:2:3 ⋍17:72:11. 4 is photostable relative to 1–3. The perdeuterobenzophenone triplet photo-sensitization with λ 366 nm at -50° of 1 leads to 3 as the sole primary product, which isomer on triplet sensitization yeilds both 1 and 2. The triplet sensitized conversion is much faster for (Z)- than (E)-β-ionone. On starting with either 1 or mixtures of 2 and 3, eventually the same photo-stationary state is obtained, viz 1:2:3⋍39:46:15. (Z)-retro-λ-ionone 4 is not formed in the triplet sensitized irradiations of 1,2 and 3 and in the direct irradiation it apparently results from the singlet excited state of the three substrates. The UV spectrum of the (unstable) (Z)-β-ionone 3 has been indirectly determined; its absorption occurs at lower wavelength and is of lower intensity than that of the (E)-isomer 1.

Sulfonation of alkenes with an excess of sulfur trioxide; stereospecific formation of carbyl sulfates

Abstract Sulfonation of the α- and internal alkenes 1a - d with an excess of sulfur trioxide initially yield stereospecifically the β-sultones 2a - d and subsequently the carbyl sulfates 3a - d via stereospecific SO3 insertion.

Photochemistry of β, γ-unsaturated ketones-V1: The direct irradiation of some γ-phenyl β, γ-enones2

Abstract The photochemistry of some members of the two series of γ-phenyl substituted acyclic β, γ-unsaturated ketones 1 and 2 upon direct irradiation with γ 310nm has been investigated, viz 1c–1h and 2b+2c.The alkyl substituted (E)-5-phenyl-4-penten-2-ones 1c–1h yield the corresponding 1,3-acyl shift products and (Z)-isomers, and 1g and 1h in addition two decarbonylated products. 2b only yields the (Z)-isomer and some benzaldehyde, but 2c yields the 1,3-acyl shift product, the ODPM product, three hydrocarbons formed by disproportionation of the allyl radical, and some benzaldehyde. The β-phenyl β, γ-UK 3a proved to be photostable. The 1,3-acyl shift products of 1c–1h result mainly from the singlet excited state in a cage radical process. The exclusive formation of the (E)-configuration of the 1,3-acyl shift product is explained in terms of conformational preference of the intermediate allyl radical. It is proposed that the formation of the (Z)-isomer proceeds from 1T(π -π*) which is populated according to . Evidence is presented which supports the proposed mechanism. The β,γ-UK 2b containing a benzoyl moiety leads to a higher degree of (E)-(Z) isomerization than the corresponding 1d which has an acetyl moiety. The triplet energies of (E)- and (Z)-1h are 56 and ca 70 kcal/mol respectively.

Sulfonation of alkenes with sulfur trioxide; reversible stereospecific β-sultone formation

Abstract The small differences in the rate coefficients of β-sultone formation between the internal and the terminal double bond in the octenes 2a-c and (Z)-1,10-nonadecadiene are evidence for a concerted cycloaddition of sulfur trioxide. The formation of β-sultone 1d is accompanied by 15% of 2-octene-1-sulfonic acid, formed in a primary side-reaction. The sulfonation of the octenes 2a-d to their β-sultones 1a-d is reversible. Desulfonation of the β-sultones 1a-d by water to the olefins 2a-d proceeds in a stereospecific syn fashion.

Photochemistry of α-oxo-oximes. Part 4. Spectral properties, conformations, and photoisomerization of α-oxo-oximes and their acetates

The α-oxo-oximes (1a–j) and (3a) and some of their esters have been prepared by ground state chemistry. In all cases the (E)-isomers were formed, except for (3a)(which was a mixture of E and Z). The (Z)-isomers of (1b–e) were obtained by irradiation of the corresponding (E)-isomers. The configurational and conformational structure of the various compounds has been assigned on the basis of n.m.r. (1H and a.s.i.s.), i.r., and u.v. data. (E)- and (Z)-(3) have a fixed OC–CN structure. The (E)-isomers of the acyclic compounds exist in the OC–CN s-trans conformation which is twisted (i.e. non-planar) for the compounds which contain a phenyl adjacent to the carbonyl group. The (E)-isomers of compounds with a phenyl adjacent to the iminyl carbon have a dihedral angle of ca. 40° between the phenyl and the nodal plane of the iminyl group as a result of repulsion between the phenyl and the oxime oxygen. The (Z)-isomers of the acyclic compounds also exist in the OC–CN s-trans conformation which is non-planar due to repulsion between the oxime oxygen and the group bound to the carbonyl carbon. However, the phenyl is now fully conjugated with the iminyl group. The cyclopropyl group of (1e) has the bisected orientation relative to the carbonyl group s-trans for (E)-(1e) and s-cis for (Z)-(1e). Irradiation of the α-oxo-oximes (1b–e), (1j), and (3a), and of the acetates (2b–e), (2j), and (3b) leads to E–Z isomerization with formation of a photostationary state. The (E)-isomers of the oximes (1a), (1f–i) and of the acetates (2a, f, and h) and (4a–c) did not photoisomerize.

Sulfonation of Alkenes by Chlorosulfuric Acid, Acetyl Sulfate, and Trifluoroacetyl Sulfate

An exploratory study has been made on the reaction of a number of non-branched alkenes in [D]chloroform as an aprotic solvent, using chlorosulfuric acid as reagent both in the presence and the absence of [D8]1,4-dioxane as complexing agent. Reaction of cyclopentene (1a) with 1.1 mol-equiv. of chlorosulfuric acid in [D]chloroform in the presence of 2.2 mol-equiv. of [D8]1,4-dioxane at 0 °C yielded quantitatively 1,2-cyclopentanesultone (2a). Under similar reaction conditions, the linear alkenes 1b–g afforded the corresponding β-sultones 2b–g. The ClSO3H–dioxane complex acted as a sulfonating reagent with the alkenes to yield the corresponding β-sultones in a syn cycloaddition of SO3 to the Carbon-Carbon double bond. In the absence of [D8]1,4-dioxane the reaction of the linear alkenes 1a–1k in [D]chloroform with chlorosulfuric acid at –40 °C led to the formation of the sec-alkyl chlorosulfates 5a–i, which were formed after initial protonation of the alkene by the strongly acidic ClSO3H. Cyclopentyl chlorosulfate (5a) in [D]chloroform at 0 °C was quantitatively converted into 1,2-cyclopentanesultone (2a). The sec-alkyl chlorosulfates 5b–i at 0 °C gave rise to a mixture of the internal trans- and cis-β-sultones 2b–m. Reaction of 1-octene (1g) with both acetyl sulfate (6a) and trifluoroacetyl sulfate (6b) as reagent in [D]chloroform at –20 °C directly afforded the products 1,2-octanesultone (2g), and the (E) and (Z) isomer of 2-octene-1-sulfonic acid (4g).

Sulphonation of polymethylbenzensulphonic acids: Evidence for a buttressing effect

Abstract The rate of sulphonation of a series of polymethylbenzene sulphonic acids in 99·6 % H2SO4 has been determined at 25·0°. The observed rate order for the various substrates (2,3,4-Me3 > 2,4-Me2 > 2,3-Me2 > 2,4,5-Me3 = 2,4,6-Me3 > 2-Me > 4-Me) is explained in terms of steric and electronic effects of the Me substituents on the rate of formation and the rates of decomposition of the σ-complex intermediate The relatively low reactivity of 2,4,5- and 2,4,6-trimethylbenzenesulphonic acid is ascribed to a very low rate of conversion of the σ-complex into the sulphonic acid product due to buttressing of the Me group ortho to the reaction centre at position 2 by the sulphonic acid substituent at position 1. For the sulphonation of benzenesulphonic acid and p-xylene-sulphonic acid in 104·4% H2SO4 at 25° the ratio of para- to meta- and of 6- to 5-substitution are 0·030 and 0·078 respectively; the corresponding activation parameter differences are ΔH≠p − ΔH≠m = 2·2 ± 0·2 kcal/mole, ΔH≠6 − ΔS≠5 = 2·4 ± 0·1 kcal/ mole, ΔS≠p − ΔS≠m = 1·3 ± 0·7 eu and ΔS≠6 − ΔS≠5 = 3·0 ± 0·4 eu. The entropy difference data illustrate that the steric requirements are smaller for sulphonation ortho to an isolated Me group than to a Me group which is flanked by an ortho-sulphonic acid group.