lecture 4 Flashcards
1
Q
what is the formula for unit of saturation?
A
(2C +2 + N - H -X) /2
2
Q
what is the problem with Kekule structure
A
- bond length: C-C bond in benzene has different bond
length from single bond and double bond - bond energy: the heat of hydrogenation is -209 kj/mol which is different from three c=c bond
- reactivity: the double bonds in benzene don’t react like typical alkenes
3
Q
how many pi-MOs does benzene have?
A
3 pi bonding MOs
3pi antibonding MOs
4
Q
what is the criteria for aromaticity?
A
- monocyclic
- planar
- 4n+2 pi-electrons (n=0,1,2,3,4,…)
5
Q
which MO would pi-electrons in aromatic compounds fill in?
A
aromatic compounds have pi-electrons only in pi-bonding MOs.
6
Q
why aromatic compounds are more stable than anti aromatic compounds?
A
bond order is directly proportional to the stability of compound. in aromatic compounds bond order is maximum, because all electrons go in bonding orbitals and are all paired.
