Kinetic P-deuterium isotope effects for solvolysis of 1-methyl cyclopentyl chloride in an ethanol + water mixture

Ross ELMORE ROBERTSON A N D EDWARD WONG Department of Chemistty, Urliversity of Calgary, Calgary, Alto., Canada T2N IN4

JOHN MARSHALL WILLIAM SCOTT Departmetlt oj'Chetnistr~~, Menlorial Ut~iversity, SS Johtz's, Nfld., Canada AIC 5S7

A N D

MICHAEL JESSE BLANDAMER, REHMAT KHAN, A N D CLIVE JOHNSON Departt,~etlt of Chemistry, University of Leicester, Leirester LEI 7RH, Et~glnnd

Received March 3, 1982'

Ross ELMORE ROBERTSON, EDWARD WONG, JOHN MARSHALL WILLIAM SCOTT, MICHAEL JESSE BLANDAMER, REHMAT KHAN, and CLIVE JOHNSON. Can. J . Chem. 61, 116 (1983).

Kinetic data are reported for the solvolysis of 1-methyl cyclopentyl chloride in a 50% by volume ethanol + water mixture. These data are combined with kinetic data for solvolysis of three deuterated analogues; I-methyl-d3 cyclopentyl chloride, I-methyl-2,2,5.5-d4 cyclopentyl chloride, and 1-methyl-d3-2,2,5,5-d, cyclopentyl chloride, being the d3, d4, and d7 derivatives respectively. The kinetic data are used to calculate the kinetic deuterium isotope effect, k H / k D . For these systems, the d,-isotope effect is close to the product of the d3 and (i4 effects.

Ross ELMORE ROBERTSON, EDWARD WONG, JOHN MARSHALL WILLIAM SCOTT, MICHAEL JESSE BLANDAMER, REHMAT KHAN et CLIVE JOHNSON. Can. J . Chem. 61, 116 (1983).

On rapporte les donnees cinitiques de la solvolyse du chlorure de methyl-l cyclopentyle dans un melange i 50% en volume d'tthanol et d'eau. On a combine ces donnees aux donnees cinktiques de la solvolyse de trois analogues deuteres: le chlomre de mkthyl-1-d3 cyclopentyle, le chlomre de methyl-l cyclopentyl-2,2,5,5-d4 et le chlorure de m6thyl-1-d3 cyclopentyl-2,2,5,5- d4, ces composCs ayant respectivement 3,4 et 7 atomes de deuterium. On a utilisC les donnees cinktiques pour calculer I'effet isotopique du deuterium, k H / k D . Pour ces systkmes, l'effet isotopique-d7 est voisin du produit des effets d3 et d,.

[Traduit par le journal]

Quite generally, P-deuterium substitution leads to a decrease Results in rate constant for a solvolytic S, reaction (1). W e have mea- The solvent was a 50% mixture of ethyl alcohol and water. sured the kinetic deuterium isotope effects for solvolysis of The kinetics of solvolysis, followed by measuring the change l - m e t h ~ l c ~ c l o ~ e n t ~ l chloride deuterated at the 1-methyl in electrical conductance (2), obeyed first order kinetics group, d,, at the methylene groups in the 2 and 5 positions, 4, (Table 1). and at both methyl and 2- and 5-methylene groups, d,.

TABLE 1. Kinetic data for the solvolysis of 1-methylcyclopentyl chloride in 50:50 by volume ethyl alcohol + water mixture

7- (K) 10, k (s-I) T (K) 10, k ( s - I ) T (K) 10' k ( s - ~ )

1-Methylcyclopentyl chloride I -Methyl(d3)-derivative 1-Methyl(d3)-2,2,5 ,5-d,-derivative 268.147 3.636 268.147 2.740 268.141 1.219 273.105 7.173 273.101 5.413 273.101 2.429 274.150 8.21 1 277.155 9.200 277.147 4.200 276.150 10.67 279.161 11.88 279.160 5.457 277.158 12.22 281.155 15.25 281.153 7.033 278.151 13.84 283.155 19.42 283.151 9.021 279.157 15.76 288.150 16.67 280.152 17.79 1-Methyl-2,2,5,5-d,-derivative 281.154 20.20 268.150 1.615 282.147 22.66 273.103 3.212 283.159 25.87 277.145 5.523 288.143 47.07 279.157 7.185

281.153 9.204 283.162 11.81 288.153 21.65

'Revision received September 8, 1982.

0008-4042/83/0 10 1 16-02$0 1 .00/0 01983 National Research Council of CanadalConseil national de recherches du Canada

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ROBERTSON ET AL. 117

Discussion In the solvolysis of 1-methyl cyclopentyl chloride, nucleo-

philic displacement of chloride occurs at a tertiary carbon cen- tre and the most obvious comparison is with the kinetic data for tert-butyl chloride in the same solvent mixture (3). Indeed the isotope effect per d-atom on the 1-methyl(d3) cyclopentyl compound is 1.099 at 283 K (i.e. 3 m ) , which is close to that calculated for tert-butyl chloride, 1.1 1 (i.e. '-1. The corresponding value for the d-atoms at the 2 and 5 positions is quite different, 1.23, and must reflect the constraint imposed by the cyclopentyl ring on the conformational changes during the displacement process. It is noteworthy, however, that the overall isotope effect in the &derivative is, over the measured temperature range, within 4% of that predicted by the products of the d3 and d, kinetic isotope effects. In other words, the isotope effects are additive with respect to their contributions to the activation Gibbs function, A G * (see Fig. I ) .

Experimental I-Methylcyclopentanol was prepared from cyclopentanone using

the Grignard reaction. The chloride was prepared by passing dry HCI through the solution at 263 K. The 2,2,5,5-d, derivatives were pre- pared from cyclopentanone-d4. The latter was prepared by warming together cyclopentanone and D20 in the presence of a trace amount of K2COs. The deuterated cyclopentanone was reduced to the alcohol (4) with 82% yield and better than 93% isotopic substitution. The I-methyl(ds) derivatives were prepared by well-established mod- ifications to the above synthetic methods.

1 . V. J. SHINER, JR. In Isotope effects in chemical reactions. Edited I I I I t ~ y C. J. Collins and N. S. Bowman. Van Nostrand Reinhold Co., - 10 0 10

New York, NY. 1970. Chapt. 8. 2. R. E. ROBERTSON. Prog. Phys. Org. Chem. 4, 213 (1967).

( T-273.15)/K 3. L. HAKKA, A. QUEEN, and R. E. ROBERTSON. J. Am. Chem. FIG. 1. Kinetic deuterium isotope effects for 1-methyl cyclopentyl

SOC. 87, 161 (1965). chloride; (a) 1-methyl(ds) derivative, (b) -2,2,5,5-d, derivative, and 4. A. STREITWEISER, J R . . R. H. JAGOW, R. C. FAHEY, and S. (c) I-methyl(d,)-2,2,5,5-d4 derivative. Curve c is drawn through the

SUZUKI. J. Am. Chem. Soc. 80, 2326 (1958). points predicted by the products of values given by curves a and b.

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