Paul Walden, the brilliant son of a farmer succeeded in finding a concept that is now widely known as umbrella effect in S_N2 reactions. In an S_N2 reaction, the configuration at the reaction centre is inverted as a umbrella turns inside out in a strong wind. An ideal S_N1 reaction, on the other hand, yield nearly racemised product as it proceeds through planar carbocation. S_N2 reactions proceed smoothly on primary alkyl halide whereas tertiary halides are fit for S_N1 mechanism. However, evidences indicate that all the molecules of particular substances do not necessarily react by a single mechanism.After all, the intention of the molecule is very clear, they want to follow the low energy path.If both paths have nearly the same energy barrier, then follow a mixed mechanism.For example, secondary alkyl halides follow a mixed mechanism, say 60% molecule react by S_N2 and rest 40%by S_N1 Stereochemical features, as mentioned above, are noticeable only when the reaction is carried out on a particular enantiomer.Even the reaction centres, which are paths of suitably substituted rings, also exemplify the said features. A reaction gives the following results. What should be the % age of back side attack assuming complete reactions ?

Paul Walden, the brilliant son of a farmer succeeded in finding a conc

1.	Paul Walden, the brilliant son of a farmer succeeded in finding a concept that is now widely known as umbrella effect in S_N2 reactions. In an S_N2 reaction, the configuration at the reaction centre is inverted as a umbrella turns inside out in a strong wind. An ideal S_N1 reaction, on the other hand, yield nearly racemised product as it proceeds through planar carbocation. S_N2 reactions proceed smoothly on primary alkyl halide whereas tertiary halides are fit for S_N1 mechanism. However, evidences indicate that all the molecules of particular substances do not necessarily react by a single mechanism.After all, the intention of the molecule is very clear, they want to follow the low energy path.If both paths have nearly the same energy barrier, then follow a mixed mechanism.For example, secondary alkyl halides follow a mixed mechanism, say 60% molecule react by S_N2 and rest 40%by S_N1 Stereochemical features, as mentioned above, are noticeable only when the reaction is carried out on a particular enantiomer.Even the reaction centres, which are paths of suitably substituted rings, also exemplify the said features. A reaction gives the following results. What should be the % age of back side attack assuming complete reactions ?
Answer» `65%` `30%` `35%` `85%` Solution :PERCENTAGE of BACKSIDE attack=Percentage of inversion + 1/2 (Percentage of racemisation) 70% racemisation and rest 30% inversion gives 65% backside attack.