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According to general organic chemistry the order of stability is as follows:
aromaticity > resonance > hyperconjugation > inductive effect
Since primary allylic carbocation shows resonance as well as hyperconjugation, moreover resonance is greater than any other effect then why is primary allylic carbocation less stable than tertiary carbocation.
The decreasing order of stablity of carbocations is:
aromatic (tropylium, cyclopropenyl) > benzyl > allyl > tertiary > secondary > primary
Allylic carbocations are resonance stabilized whereas tertiary alkyl groups are stabilized by hyperconjugation (and inductive effect). The hyperconjugation (and inductive effect), in general, is quite weaker than resonance (and hyperconjugation effect). The only exceptions to the previous statement I am aware of are halogens (inductive effect is stronger than resonance).
