5.10 intro to org chem

Question 1

state the hybridisation of a carbon-carbon single, double and triple bond

Answer 1

sp3, sp2, sp

Question 2

explain why C=C is shorter and stronger than C-C bond

Answer 2

C=C carbons are sp2 hybridised while C-C carbons are sp3 hybridised. C=C has a higher percentage of s character, hence it forms a shorter and stronger bond due to the s orbital being closer to the nucleus.

C=C has side-on overlap of orbitals to form pi bonds, shortening distance between carbon atoms

Question 3

what is the order of functional groups priority for naming compounds?

Answer 3

carboxylic acids > carboxylic acid derivatives > nitrile > carbonyl compounds > OH > NH > hydrocarbons

Question 4

three types of structural / constitutional isomers

Answer 4

1) chain isomerism (more cyclic)
2) positional isomerism (substituents on diff carbons)
3) functional group isomerism (diff functional groups, same formula)

Question 5

define stereoisomerism and state the two possible types

Answer 5

stereoisomerism are compounds with the same molecular and structural formula but different spatial arrangement of atoms.
cis-trans isomerism and enantiomerism

Question 6

what are the criteria for cis-trans isomerism?

Answer 6

1) restricted rotation of bond due to C=C double bond or rigid ring structure
2) different atoms/groups of atoms on EACH carbon atom in the C=C bond

Question 7

which is cis and which is trans?

Answer 7

cis has substituents on the same side, trans has substituents on different sides

Question 8

why does cis isomer have a higher boiling point than trans isomer?

Answer 8

both are simple molecular structures. however, more energy is required to overcome stronger pd-pd in polar cis isomer than weaker id-id in non-polar trans isomer, hence boiling point higher

Question 9

why does trans isomer have higher melting point than cis isomer?

Answer 9

both are simple molecular structures. however, trans isomer has higher symmetry and can pack more closely in its solid lattice structure. hence more energy is required to overcome extensive id-id during melting

Question 10

what are the criteria for enantiomerism?`

Answer 10

1) non-superimposable mirror image
2) no internal plane of symmetry
3) chiral centre (carbon attached to four different substituents)

Question 11

what are meso compounds?

Answer 11

molecues with multiple chiral centres but an internal plane of symmetry