Question

The increasing order of electron donating inductive effect of alkyl group is:
A. \[-H<-C{{H}_{3}}<-{{C}_{2}}{{H}_{5}}<-{{C}_{3}}{{H}_{7}}\]
B. \[-H>-C{{H}_{3}}>-{{C}_{2}}{{H}_{5}}>-{{C}_{3}}{{H}_{7}}\]
C. \[-H<-{{C}_{2}}{{H}_{5}}<-C{{H}_{3}}<-{{C}_{3}}{{H}_{7}}\]
D. \[-H>-{{C}_{2}}{{H}_{5}}>-C{{H}_{3}}>-{{C}_{3}}{{H}_{7}}\]

Answer 1

Hint: Alkyl groups are electron withdrawing and alkyl groups are electron donating. The alkyl group has positive inductive effect (\[+I\]effect). Hydrogen is less electronegative and carbon is more electronegative.

Complete step-by-step answer:
Partial shifting of sigma bond electrons in covalent compounds or unequal sharing of bonding electrons is known as inductive effect (I-effect). There are two effects: one is electron withdrawing (\[-I\] effect, negative inductive effect) and one is electron donating (\[+I\]effect, positive inductive effect). In alkyl groups carbon is more electronegative than hydrogen, so carbon attracts sigma bond electrons from hydrogen and shows partial negative charge on it and partial positive charge on hydrogen. So, carbon has a tendency to donate electrons that push the electrons towards other groups. All alkyl groups are electron donating groups. This electron donating tendency increases when the number of carbon increases in the alkyl group. So, the order of \[+I\] effect: \[-H<-C{{H}_{3}}<-{{C}_{2}}{{H}_{5}}<-{{C}_{3}}{{H}_{7}}\]
“A” is the correct answer.

Note: If any other more electronegative element (more than carbon) is attached with the alkyl group then it is not an electron donating group anymore and it shows \[-I\] effect. For example: Alkyl halide shows \[-I\] effect, because halogen is more electronegative than carbon.