[phoenixrising]

Rank the following compounds in order of increasing rate of hydration (1 = slowest, 5 = fastest).

3-hexanone: 1?
2,2-difluorobutanal:
2,2-dichlorobutanal: 
4-chloro-2-pentanone: 2?
3-chlorobutanal:

I don't necessarily understand how I can do this quickly... this is going to be on my Orgo test tomorrow....
I know that

Formaldehydes faster than > aldehydes faster than > ketones

That's what my teacher has in his lecture notes but there are 3 aldehydes and 2 ketones.

[discodermolide]

Quote "Formaldehydes faster than > aldehydes faster than > ketones"

Are you sure about this? It says aldehydes faster than ketones, but you have a ketone as the fastest. Something not correct here.

What effect do the substituents have on the rate of hydration?

[phoenixrising]

Quote "Formaldehydes faster than > aldehydes faster than > ketones"

Are you sure about this? It says aldehydes faster than ketones, but you have a ketone as the fastest. Something not correct here.

What effect do the substituents have on the rate of hydration?

Im pretty sure

The question says 1 = slowest, 5 = fastest.

And I think I figured it out

The answers are

3-hexanone: 1 (most slowest)
2,2-difluorobutanal: 5 (most fastest)
2,2-dichlorobutanal:  4 (second most fastest)
4-chloro-2-pentanone: 2 (second most slowest)
3-chlorobutanal: 3

I guess the concept is:
The carbonyl C bonded with the MOST and CLOSEST electronegative atoms will be the most reactive and have the fastest hydration rate which results in a larger K_hydration

[discodermolide]

My mistake, sorry.
Yes you are correct with your list.
Have a look at this page http://books.google.ch/books?id=kQgu2j_ber0C&pg=PA134&lpg=PA134&dq=electronic+effects+in+hydration+of+carbonyl+groups&source=bl&ots=AnR-X0Ejfq&sig=x6JXzCzcXsCuKITo_GHRqDL1L_8&hl=en&sa=X&ei=PBIsUZ_tIOSS4ASa5oDYDg&sqi=2&ved=0CEYQ6AEwAw#v=onepage&q=electronic%20effects%20in%20hydration%20of%20carbonyl%20groups&f=false

Read the bit after the IR spectra. It shows this effect rather well

[phoenixrising]

My mistake, sorry.
Yes you are correct with your list.
Have a look at this page http://books.google.ch/books?id=kQgu2j_ber0C&pg=PA134&lpg=PA134&dq=electronic+effects+in+hydration+of+carbonyl+groups&source=bl&ots=AnR-X0Ejfq&sig=x6JXzCzcXsCuKITo_GHRqDL1L_8&hl=en&sa=X&ei=PBIsUZ_tIOSS4ASa5oDYDg&sqi=2&ved=0CEYQ6AEwAw#v=onepage&q=electronic%20effects%20in%20hydration%20of%20carbonyl%20groups&f=false

Read the bit after the IR spectra. It shows this effect rather well

Thanks a bunch!!