dehydration에서 secondary, tertiary alcohol은 E1 mechannism에 의해 반응하고 primary alcohol은 E2 mechanism에 의해 반응한다고 되어 있는데 이유가 뭔가요? primary에서는 carbocation이 불안정해서 E1이 안 일어나는 건 알겠는데 secondary, tertiary에서는 왜 E2에 의해서도 반응이 일어나지 않는거죠? alkyl halide에서는 치환기가 증가할 수록 E1,E2 다 잘 일어나는 걸로 배웠는데 알코올은 다르네요.

alcohol을 alkyl halide로 만들 때 치환기가 많은 alcohol이 HX와 더 빠르게 반응한다고 되어 있는데 이유가 뭔가요?