Electrophilic Carbonyls

Carbonyls WITHOUT leaving groups: Reactions with H₂O

Ketones/Aldehydes reaction with H₂O

This reaction is all in equilibrium

Which is the major and minor product?

The equilibrium is heavily based to the left

Formaldehyde + H₂O

Which is the major and minor product?

There is no inductive effect here (because H is neither electron withdrawing or donating), so formaldehyde is very reactive due to its carbonyl C being very electrophilic and the water attacks it, and so the equilibrium lies to the right.

Cyclic ketone + H₂O

This is due to sterics

The 3C ring is a triangle shape. The angle in a 3C ring is 60°. There is very high ring strain therefore in the cyclic ketone, as the sp² angle is 120°.

In the product, the sp³ angle is now 109° which is closer to 60°, so there is reduced ring strain. The molecule wants to be in the hydrated form because it is “happier”

When considering why a reaction occurs, what 2 points do you have to consider?

• Steric argument

• Electronic argument

Carbonyl + Alcohol

• The H in R-OH (alcohol) protonates the O in C=O

• This makes the C=O C more electrophilic, so is very δ+

• Therefore the lone pair of electrons on the O in R-OH (alcohol) moves via curly arrow to the electrophilic C.

• Making a bond, leads to bond breaking in C=O

If R¹ = Alkyl, what is this known as?

Hemi ketal

Hemi ketal derives from a…

ketone

If R¹ = H, what is this known as?

Hemi acetal

Hemi acetal derives from an…

aldehyde

Ketone + Alcohol