CH3Br

CH3BR BROMOMETHANE -55.241 8.0199E-02 1.1207E-05 -28.16 69 C2H402 METHYL-FORMATE -350.914 1.7474E-01 1.6322E-05 -297.19... 

CH3Br -I- Y CH3Y -H Br A nucleophilic parameter WMcBr is defined... 

Another way to assess nucleophilic reactivity is to examii the shape of the nucleophile s electron-donor orbital (th is the highest-occupied molecular orbital or HOMC Examine the shape of each anion s HOMO. At which ato would an electrophile, like methyl bromide, find the be orbital overlap (Note This would involve overlap of tl the HOMO of the nucleophile and the lowest-unoccupif molecular orbital or LUMO of CH3Br.) Draw all of tl products that might result from an Sn2 reaction wi CHaBr at these atoms. 

First, look at the reaction and identify the bonding changes that have occurred. In this case, a C—Br bond has broken and a C-C bond has formed. The formation of the C-C bond involves donation of an electron pair from the nucleophilic carbon atom of the reactant on the left to the electrophilic carbon atom ol CH Br, so we draw a curved arrow originating from the lone pair on the negatively charged C atom and pointing to the C atom of CH3Br. At the same time the C—C bond forms, the C-Br bond must break so that the octet rule is not violated. We therefore draw a second curved arrow from the C-Br bond to Br. The bromine is now a stable Br- ion. 

In every chemical reaction, there is a direct relationship between the rate at which the reaction occurs and the concentrations of the reactants. When we measure this relationship, we measure the kinetics of the reaction. For example, let s look at the kinetics of a simple nucleophilic substitution—the reaction of CH3Br with OH- to yield CH3OH plus Br-—to see what can be learned. 

CH3OTos > CH3Br > (CH3)2CHC1 > (CH3)3CC1 Similar to protic solvents Racemic 1-ethyl-l-methyJhexyl acetate 90.1% racemization, 9.9% inversion... 

CH3 + BrCCh CH3Br + CCI3 With mixtures of the two, the product ratio can be expressed as... 

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