Organic Chemistry 1.2 - Molecular Orbitals - Hybridisation in Alkenes, Benzene, and Alkynes

Question 1

In alkanes the bonding can be described by ___ hybridisation.
In alkenes the bonding can be described by ___ hybridisation.
In alkynes the bonding can be described by ___ hybridisation.

Answer 1

sp3.
sp2.
sp

Question 2

sp3 hybridisation involves the hybridisation of…
sp2 hybridisation involves the hybridisation of…
sp hybridisation involves the hybridisation of…

Answer 2

one s, three p.
one s, two p.
one s, one p

Question 3

The number of hybrid orbitals formed is…
Therefore when one s and two p orbitals hybridise…

Answer 3

equal to the number of atomic orbitals hybridised.
three degenerate hybrid orbitals form

Question 4

In alkenes, the 3 sp2 orbitals in the carbon do what?
What shape do the 3 sp2 orbitals take?
What does the remaining p orbital do?

Answer 4

overlap end-on with the surrounding hydrogens/carbons to form sigma bonds.
trigonal planar. (alkenes exist in one plane).
overlap side-on with the p orbital of another carbon, forming a pi bond

Question 5

Why do alkene bonds take less than twice as much energy to break than alkane bonds?

Answer 5

because pi bonds are weaker than sigma bonds

Question 6

Alkene bonds look like c=c.
One bond is ___, the other is ___.

Answer 6

pi, sigma

Question 7

The bonding in aromatic systems (such as ___!) can be described by ___ hybridisation.

Answer 7

benzene, sp2

Question 8

The _ carbon atoms in benzene are arranged in a ___ structure with ___ bonds between the carbons.

Answer 8

6, cyclic, sigma (all single bonds)

Question 9

In benzene, the unhybridised p orbitals on each carbon do what?

Answer 9

overlap side on to form a pi molecular system which is perpendicular to the plane of the sigma bonds.

Question 10

The pi molecular system is…

Answer 10

a cloud of 6 delocalised electrons which extends across all 6 carbon atoms

Question 11

The bonding in alkynes can be explained by…
Explain it.

Answer 11

sp hybridisation.
In each carbon atom, one s and one p orbital hybridise, forming two sp hybrid orbitals, which allows it to make two sigma bonds to different atoms. The remaining two p orbitals that did not hybridise overlap side-on with other p orbitals, forming two pi bonds. Hence the triple bond between carbons (one sigma, two pi) .