the grunwald - winstein equation ( equation 1 ) was originally developed   in 1948 for the correlation of specific rates of solvolysis of initially neutral substrates reacting by an ionization ( sn1 + e1 ) mechanism . in equation 1 , k and ko are the specific rates of solvolysis in a given solvent and in the standard solvent ( 80% ethanol ) , respectively , m represents the sensitivity to changes in the solvent ionizing power y ( initially set at unity for tert - butyl chloride solvolyses ) , and c is a constant ( residual ) term .
it is now realized both that the scales are leaving - group dependent and that adamantyl derivatives provide better standard substrates , and a series of yx scales are available .
it was immediately realized that bimolecular ( sn2 and/or e2 ) reactions can not be expected to follow such a relationship because solvent nucleophilicity ( n ) will also be an important factor .
however , for a given type of binary solvent ( such as a series of aqueous - ethanol mixtures ) a linear plot based on equation 1 was frequently observed due to collinearity between the n and y scales .
such plots had m values considerable lower than unity and these values were taken as evidence for a bimolecular reaction .
it was further realized   that , in principle , the correlation could be extended ( equation 2 ) to include a term governed by the sensitivity  to changes in solvent nucleophilicity ( n ) .
however , in practice , an n scale could not be developed because the appropriate m value for insertion into the equation (  = 1 for the standard substrate ) could not be obtained .
schleyer and bentley   estimated the m values at 0.3 for the solvolyses of methyl p - toluenesulfonate , and arrived at the nots scale . at the present time ,
scales are usually based on the solvolyses of s - methyldibenzothiophenium ion , in which the leaving group is a neutral molecule , which is little influenced by solvent change , and the my term can be neglected .
the nt values obtained   indicated that the m for methyl p - toluenesulfonate is best set at 0.55 and revised nots values are in good agreement with nt values .
when aromatic rings are bonded , at the transition state , to the carbon which is developing positive charge , the charge will be partially distributed into the aromatic rings .
this causes changes in the solvation of the rings in going from the substrate to the activated complex , which in turn leads to a perturbation of analyses in terms of equation 1 or 2 .
this can be accommodated by use of similarity model scales in which the standard substrate contains similarly situated aromatic rings   and new ionizing power scales are devised .
alternatively , a third variable term can be added to the linear free energy relationship ( equation 3 ) , governed by the sensitivity h to changes in the aromatic ring parameter ( i ) .
the development and uses of extended forms of the grunwald - winstein equation was recently   reviewed in more detail than is presented in this manuscript . in recent correlations , using the three forms of the grunwald - winstein equation ( equations 13 ) , evidence was found for a modest hi contribution in the solvolyses of n , n - diphenylcarbamoyl chloride even although the aromatic rings are not directly attached to the carbon at the reaction center .
this gave support to the claim by liu , based on both experimental and theoretical considerations , that in these solvolyses positive charge is transferred to the aromatic rings through contributions from non - canonical resonance structures .
if such an effect can be operative in the solvolyses of aromatic carbamoyl chlorides ( ar2ncocl ) , it could also be present in the solvolyses of aromatic chloroformate esters ( arococl ) , such as p - methoxyphenyl chloroformate ( 1 ) or phenyl chloroformate ( 2 ) .
while the h value of 0.35  0.19 was essentially negligible for 2 , a much larger value of 0.85  0.15 was calculated for 1 .
however , it was pointed out that the 31 solvents used in the analyses of the specific rates of solvolysis of 1 included only two with a fluoroalcohol component .
fluoroalcohols are extremely important , either as pure solvents or as a component of binary mixtures , in studies leading to analyses in terms of the grunwald - winstein equations [ 1315 ] .
accordingly , it was suggested   that a more detailed investigation of the solvolyses of 1 was desirable . in this contribution
we have augmented the study of the specific rates of solvolyses of 1 by adding additional solvents , with almost all of them having an appreciable fluoroalcohol component .
values for the specific rates of solvolyses at 25.0 c were previously available for 31 pure and binary solvents   and 13 additional values , presented in table 1 , have been determined .
correlations with all 44 solvents are considerably improved , primarily due to an improved variety of solvents , as regards the relationship between nt and ycl values , and only secondarily due to an increase in the number of data points . of the binary mixtures with water ,
five involve an appreciable proportion of 2,2,2,-trifluoroethanol ( tfe ) and four an appreciable proportion of 1,1,1,3,3,3- hexafluoro-2-propanol ( hfip ) .
table 1 also includes the additional nt , ycl , and i values needed within the correlation analysis .
a major goal of the analyses is to examine the extent of the improvement ( if any ) in going from application of equation 2 to application of equation 3 , involving the absence or presence of the hi term .
the results of the correlations are presented in table 2 . for comparison , the results reported earlier   for the solvolyses of 1 in 31 solvents and for the solvolyses of 2 in 49 solvents are both included in the table .
also , the correlation of the specific rates of solvolysis of 2 is reported with restriction to exactly the same 44 solvents used in the correlation with 1 as the substrate .
the correlation of the specific rates of solvolysis of 1 gave a good correlation in terms of equation 2 ( figure 1 ) , which showed virtually no improvement in the multiple correlation coefficient ( 0.981 to 0.982 ) on advancing to the application of equation 3 .
in particular , the h value of 0.29  0.18 was much lower than the 0.85  0.15 reported for 31 solvents and it was associated with a large ( 0.114 ) probability that the hi term was statistically insignificant . with the application of equation 2 ,
the multiple correlation coefficient improves considerably ( 0.964 to 0.981 ) on inclusion of the 13 data points from table 1 .
the values in table 2 illustrate the need for a good selection of solvents for a meaningful application of extended forms of the grunwald - winstein equation .
the observed  and m values are within the range previously observed for other reactions at acyl carbon which are believed to proceed by an addition - elimination ( association - dissociation ) mechanism ( shown for 1 in scheme 2 below ) , with the addition step rate - determining . for solvolyses of 2 ,
the  and m values change only slightly on reducing the number of solvents from 49 to 44 , so as to correspond to the study with 1 as the substrate .
the already lower value for h ( 0.35  0.19 ) becomes slightly lower ( 0.19 + 0.20 ) on limiting to 44 solvents . in comparing the specific rates of solvolyses of 1 and 2 in these 44 solvents ,
this observation suggests that a very good direct linear relationship should exist between their specific rates of solvolysis .
it can be seen from figure 2 that this is indeed the case and a plot of log ( k / ko ) values for 1 against those for 2 gives an excellent linear plot with a correlation coefficient of 0.998 , f - test value of 9302 , slope of 0.991 + 0.010 , and intercept of 0.075 + 0.015 .
the presently reported analyses strongly support the proposal of very similar mechanistic characteristics for the solvolyses of 1 and 2 .
they demonstrate that the previous indication   of a meaningful hi contribution associated with the extended grunwald - winstein treatment of 1 but not of 2 was , as suspected at the time , an artifact , resulting from an inadequate selection of solvents being available when the specific rates of solvolysis of 1 were treated in terms of equation 3 . with the addition of data for the solvolysis in several fluoroalcohol - containing solvents ,
the linear free energy relationship behavior becomes essentially identical to that previously observed for 2 .
solvents were purified and the kinetic runs carried out as described previously . a substrate concentration of approximately 0.03
the calculation of the specific rates of solvolysis ( first - order rate coefficients ) used the experimental infinity titers , at about ten half - lives , except for the runs in 97% hfip , when portions were added to equal volumes of water and allowed to stand for 4 weeks prior to the usual titration of developed acid , and for the runs in 97% tfe , when the conventional guggenheim treatment   was modified   so as to give the infinity titer , which was then used to calculate for each run a series of integrated rate coefficients .
the specific rates and associated standard deviations , as presented in table 1 , are obtained by averaging all of the values from , at least , duplicate runs .
 a recent correlations analysis of the specific rates of solvolysis of p - methoxyphenyl chloroformate ( 1 ) in 31 solvents using the three - term grunwald - winstein equation led to a sensitivity ( h ) towards changes in the aromatic ring parameter ( i ) of 0.85  0.15 . 
 this value , suggesting an appreciable contribution from the hi term , is in contrast to the h value of 0.35  0.19 that was reported for the parent phenyl chloroformate ( 2 ) . 
 however , for 1 , only two specific rate values were available for the important fluoroalcohol containing solvents . 
 values are now reported for 13 additional solvents , 12 of which have appreciable fluoroalcohol content . with all 44 solvents considered , it is found that the solvolytic behavior indicated for 1 now parallels very closely that previously reported for 2 . 
1. Introduction
2. Results and Discussion
3. Conclusions
4. Experimental Section