# Extent of dehydration by conc sulphuric acid

I know that conc $\ce{H2SO4}$ is dehydrating agent. And the most easiest mechanism example would be this,

But ,I want to know how to find theextent of dehydration of it. I came across this question

my thinking- (a) $O$ is EN and will pull $-OH$ towards itself inductively, thus decreasing the electron density on $-OH$ ,and decreasing its power to pull $H$ from conc $\ce{H2SO4}$.

Similarly for (b) and (c) and I think due inductivity (c) will have more chances than (b)

As for the (d) I think $-CH3$ group is a pusher so it should increase the electron density, and hence reducing the effect on $-OH$ group .

1)but my doubt is ,is this the only reason for the extent of dehydration by conc $\ce{H2SO4}$ on (d) to be more than (c)

2) I don't think there would be much difference if it tautomerises to enol form ?

• The extent of dehydration would relate to how much hydrate the starting material could potentialy form with the sulfuric acid? – Technetium Oct 28 '15 at 13:53
• Could you please tell in more detail? – shaistha Oct 28 '15 at 14:40
• You should think about the relative stabilities of the products. Which has the most stable dehydration product and why? – bon Oct 28 '15 at 15:13
• I'll give you two more hints. (1) You must think in 3D. The ring on the molecule isn't flat. (2) a,b and c have OH moved relative to C=O group. The OH would have the most effect "meta" or "ortho" to the C=O, so b is very likely out off the bat. – MaxW Oct 28 '15 at 19:03
• @MaxW thank you, it kind of helped. But I want to know why d over c? Is the reason what I have already written or something else. If I'm wrong, then please tell me where I'm wrong or I'm missing here. – shaistha Oct 28 '15 at 21:24