# Can this sp2 lone pair resonate?

In methyl isocyanate, $$\ce{CH3CNO}$$, shown below,

it seems that the nitrogen lone pair can resonate with the carbon oxygen double bond, generating a resonance structure something like acetonitrile oxide:

In that case, why is the geometry around the nitrogen in the methyl isocyanate compound bent and not linear? Can the lone pair even resonate like that?

I remember in Klein's organic chemistry, it is stated that

Whenever an atom possesses both a π bond and a lone pair, they will not both participate in resonance

In methyl isocyanate, $$\ce{CH3CNO}$$, shown above, it seems that the nitrogen atom has both a π bond and a lone pair. So perhaps the sp2 lone pair on nitrogen atom cannot resonate with the carbon oxygen double bond? I am not sure.

• I don't understand the title. Vinyl is CH2=CH-. It has no lone pair ! – Maurice Dec 29 '19 at 16:48
• @Maurice I mean vinyl as in lone pair on a double bond (such as in N) – Cyclopropane Dec 29 '19 at 16:49

Whenever an atom possesses both a π bond and a lone pair, they will not both participate in resonance

The sentence means that only one, either the 𝜋 bond or the lone pair will participate in resonance if the atom has both.

For example, in a pyridine, the nitrogen has a lone pair and it is also attached to a 𝜋 bond.

Here, however, only the 𝜋 bond participates in resonance because it is in the plane perpendicular to the molecule, while the lone pair is not.

Methyl isocyanate is best represented by a group of three resonance structures:

Here is the 3D structure of the most significant resonance structure of methyl isocyanate:

• So C and O are both sp2 hybridized? – Cyclopropane Dec 29 '19 at 18:53
• The first Carbon is sp3, the second sp. The oxygen atom must have either sp2 or sp hybridization, because it needs a p orbital to participate in the C–O π bond. This oxygen atom has three attachments (the carbon and two lone pairs), so we use sp2 hybridization. – Shootforthemoon Dec 29 '19 at 19:01
• Did this answer ur question? @DrPepper – Shootforthemoon Dec 29 '19 at 19:25
• kind of? I know in amides the N looks sp3 but it is actually sp2 because it is conjugated to the carbonyl, so I was wondering why that doesn't happen here. The N looks like it should be sp2, but if this resonance works, it would be sp because of conjugation to the C=O in H3CNCO – Cyclopropane Dec 29 '19 at 20:27
• @DrPepper Well, look at the most significant structure, N is hybridized sp2. When an atom that appears to be sp3 hybridized can participate in resonance, that atom is in fact sp2 hybridized. This is because resonance requires an open p-orbital to occur. Sp3 atoms have 4 sp3-hybridized orbitals but no open p-orbitals, and therefore cannot participate in resonance, while sp2-hybridized atoms can. – Shootforthemoon Dec 29 '19 at 20:37