The Electron Withdrawal Power of Substituent Groups

ethane 25 "C, on a mesurC la vitesse d'addition du chlorure de dinitro-2,4 benzenesulfknyle B des phCnyl-1 prop'enes cis et tratls substituCs sur le noyau aromatique par des nitro-3, chloro-4, mCthyl-4, mCthoxy-4, phknoxy-4 et isopropoxy-4; on a aussi dCterminC la stCrCochimie des produits. Alors que l'on obtient une relation linbire entre log k2 vs. soit u ou U+ on obtient une meilleure correlation avec U . On obtient une telle relation linhire m&me si la stCrCochimie des produits change de stCreospkifique et nonrkgiospkifique pour les substituants Clectro-attracteurs (nitro-3 et chloro-4) h regiospkifique et non stCrCospCcifique pour les substituants Clectro-donneurs (mkthoxy-4, phCnoxy-4 et isopropoxy-4). Les rksultats suggkrent que 1'Ctape dkterminante, pour toutes ces additions, est un ion ponte et que tous les ions ouverts se forrnent aprks cette Ctape.[ The rate of addition of 2,4-dinitrobenzenesulfenyl chloride to cis and t~atls 3-NO2, 4-CI, 4-CH3, 4-OCH3, 4-OCsHs, 4-0CH(CH3)2 substituted-1-phenylpropenes has been measured in 1,1,2,2-tetrachloroethane at 25 "C and the product stereochemistry has also been determined. While a plot of log k2 vs. either u or U+ is linear a better correlation is obtained with U . Such a linear relationship is obtained even though the product stereochemistry changes from stereospecific and nonregiospecific for electron-withdrawing substituents (3-N02, 4-CI) to regiospecific and nonstereospecific for electron-donating substituents (4-OCH3, 4-OCsHs, and 4-0CH(CH3)2). These results suggest that the rate determining step for all the additions is bridged and that any open ion is formed after this step.The recent report of the addition of 2,4-dinitrobenzenesulfenyl chloride to cis-and transanethole is the first example of a nonstereospecific addition of an arenesulfenyl chloride to an alkene (2). In this reaction an open carboniuin ion is clearly involved as an intermediate prior to the product determining step. However it is not clear if the first formed intermediate is also an open carbonium ion. In an attempt to obtain more information about the mechanism of this reaction we have examined the rate of addition of 2,4-dinitrobenzenesulfenyl chloride to a series of phenyl substituted cis-and trans-l-phenylpropenes (la-g and 20-g).The purpose of this study is to determine if there is a break in the Harnmett crp plot at the point where the addition becomes nonstereospecific. In this way, we should be able to determine if there is a change in the structure of the rate determining transition state as the product stereochemistry changes. ResultsThe rates of addition of 2,4-dinitrobenzenesulfenyl chloride to a series of phenyl substituted cis-(la-g)-and trans-(2a-g)-1-phenylpropenes were measured at 25 "C in 1,1,2,2-tetrachloroethane (TCE) by two methods: a titrimetric method and a dilatometry method using an Anton Paar precision density meter. The additions were found to exhibit normal second-order kinetics, first-order in alkene and first-order in sulfenyl chloride to 80% completion o...

Section: Resultssupporting

confidence: 62%

The addition of 2,4-dinitrobenzenesulfenyl chloride to a series of phenyl substituted cis- and trans-1-phenylpropenes

Sçhmid¹,

Nowlan²

1976

“…The basis of this method 4-chlorobenzenesulfenyl chloride to alkenes. is that protons a or 0 to chlorine are considerably deshiclded relative to those a or to sulfur Results (10,11). The nii~r parameters of the adducts We have measured the rate of addition of 4-obtained in this study are reported in every case it was possible to find at least one nonoverlapping signal from which the isomer distribution could be calculated.…”

Section: +1mentioning

confidence: 83%

The effect of alkene structure upon the rates and product composition of addition of 4-chlorobenzenesulfenyl chloride

Sçhmid¹,

Dean²,

Garratt³

1976

The rates and products of addition of 4-chlorobenzenesulfenyl chloride to 30 mono- and disubstituted alkenes have been determined in 1,1,2,2-tetrachloroethane at 25 °C. The rates of addition span a range of 106. No correlation with the extended Taft equation was found with the rates of all 30 compounds. The rate ratio kc/kt for addition to nine pairs of isomeric cis-trans alkenes ranges from a low of 3.1 for the 2-butenes to a high of 1.57 × 105 for the 2,2,5,5-tetramethyl-3-hexenes. The rate ratio kc/kt does not always increase regularly with the increasing size of the substituents which suggests that relief of ground state strain is not important in the rate determining transition state. Greater steric hindrance between the electrophile and the trans alkene compared to the cis isomer is proposed to account for the results.

“…Recent and detailed studies of benzyl chloride (13b), benzyl fluoride (13a), and derivatives of benzyl methyl ether (32) yield '~9 0 as -1.06, -0.95, and -1.02 Hz, respectively, for these compounds. On a scale on which the electronegativities of H, C1,O-R, and F are 1.78,3.0, 3.3 1, and 3.92, respectively, the electronegativity of SH is 2.5 (33)(34)(35) and yields 6~9 0 as -1.12 Hz at 0 = 90'. It follows that (sin2 0) for benzyl thiol in CS2 solution at 300 K is 0.359, that the preferred conformer has 0 = 30°, as in 10, and that V2 is 7.0 kJ/mol.…”

Section: The Internal Barrier In Benzyl Thiolmentioning

confidence: 99%

The benzylic anomeric effect. Internal rotational potentials of ArCH₂X compounds (X = F, Cl, SH, SCH₃, S(O)CH₃, SO₂CH₃)

Penner¹,

Schaefer²,

Sebastian³

et al. 1987

. Can. J . Chem. 65, 1845Chem. 65, (1987. The apparent twofold barriers to rotation about the exocyclic C-C bonds in ArCH2X (X = SH, SMe, S(O)Me, S02Me) compounds have been determined in CS, and in benzene-d6, from the magnitudes of long-range proton-proton coupling constants. The work extends earlier studies of the systems X = F, C1. Except for X = F, all of the title compounds have a low energy conformation in which the C-X bond is perpendicular to the plane of the benzene ring. The introduction of two meta-chlorine substituents leads to a 2 kJ/mol relative destabilization of this structure for X = F, C1, SH. The trend in the rotational barriers associated with the sulfur substituents is SH, SMe < < S(O)Me, S02Me. Ab initio calculations, with geometry optimization at the STO-3G level for X = F, C1, SH, reproduce the experimental results, and also the magnitudes of the rotational barriers. Quantitative PMO analyses of these a b initio wavefunctions have been employed to distinguish between "steric" and "other" interpretations, and reveal that the preferred conformation of X = F is determined by a first order perturbational effect, manifested in an electrostatic attraction between the heteroatom and a syn-periplanar ortho-hydrogen. For X = C1, the PMO analysis suggests that a T T~, -u & interaction, analogous to the n -~:~ interaction postulated as the origin of the anomeric effect in heterocyclohexanes, plays a dominant role. For X = SH, both T T~~-~:~ and ucx-n:, interactions are found; the latter is not possible in the anomeric effect itself. It is concluded that a benzylic anomeric effect exists, and that its magnitude, as a function Chem. 65, 1845Chem. 65, (1987.Utilisant les amplitudes des constantes de couplage proton-proton i longue distance, on a dCterminC les barrikres binaires apparentes 21 la rotation autour des liaisons exocycliques C-C des composCs ArCH2X (X = SH, SMe, S(0)Me et S0,Me) dans le CS2 et dans le benzene-d6. Ces Ctudes sont une extension d'etudes anttrieures sur des systkmes dans lesquels X = F et C1. Except6 pour le cas oB X = F, tous les composCs mentionnCs dans le titre prtsentent une conformation de basse Cnergie dans laquelle la liaison C-X est perpendiculaire au plan du noyau benzCnique. L'introduction de deux chlores en positions me'ta conduit a une distabilisation relative de 2 kJ/mol de cette structure pour X = F, C1 et SH. Cette tendance dans les barrikres rotationnelles associCes avec les substituants contenant du soufre est la suivante : SH. SMe << S(O)Me, S02Me. Des calculs a b initio impliquant des optimisations de la gComCtrie au niveau STO-3G ont CtC rCalisCs sur les composCs contenant X = F, C1 et SH et ils permettent de reproduire les resultats expkrimentaux ainsi que les amplitudes des barrikres a la rotation. On a utilisC des analyses quantitatives PMO de ces fonctions d'onde a b initio pour distinguer entre les interpretations ste'riques et antres; ces analyses rCvklent que la conformation privilCgiCe pour X = F est dCterminCe par un effet de perturbation du pre...