Question

DBU, 1,8-diazabicyclo$\left[5.4.0\right]$ undec-7-ene, is a base we will encounter in elimination reactions in Chapter 8. Which N atom is more basic in DBU? Explain your choice.

Short answer

The ${\text{sp}}^3$hybridized nitrogen atom is the more basic in DBU.

Step-by-step solution

Properties of DBU

The DBU has two nitrogen atoms. Therefore, DBU is a strong base in organic chemistry.

Explanation

The two nitrogen atoms have different hybridization. Therefore, the basic character also differs for these two.

One nitrogen is ${\text{sp}}^3$ hybridized due to single bond pairs, and one nitrogen atom is localid="1649309090679" ${\text{sp}}^2$ hybridized due to double bond pairs.

The s character in localid="1649309105691" ${\text{sp}}^3$ hybridized nitrogen atom is 25%, whereas the s character in localid="1649309111225" ${\text{sp}}^2$ hybridized nitrogen atom is 33%. Therefore, lone pair of electrons on localid="1649309131748" ${\text{sp}}^3$ nitrogen atom is free for donation than localid="1649309139355" ${\text{sp}}^2$ hybridized nitrogen atom.

Representation of more basic nitrogen atom