The stability of Me2C=CH2 is more than that of MeCH2CH=CH2 due to:
Hyperconjugative effect of the Me group.
If I say,
→ A more substituted alkene is more stable. You will ask me why ?
Let's find out.
Stabilities of alkenes is again due to hyper conjugation.
For example,
(A)
+11 more hyperconjugative structures
(B)
+8 more hyperconjugative structures
(A) and (B) show 13 and 10 H.C. structures respectively. So (A) is more stable than (B). conversely, (B) is more reactive than (A).
Therefore, Me2C=CH2 > MeCH2CH=CH2 Because
CH3 ╲ ╱CH3C=C H╱╲ H
6 α−Hydrogen
6 hyperconjugative structures
CH3CH2 ╲ ╱HC=C H╱╲ H
=>2 α−Hydrogen
2 Hyperconjugative structures
∴Me2C=CH2>MeCH2CH=CH2 (stability)