Lecture 2 - Chemistry of Alkanes

Question 1

two classes of hydrocarbons:

Answer 1

aliphatic and aromatic

Question 2

define the 4 C’s

composition:
constitution:
configuration:
conformation:

Answer 2

composition: what elements does it contain (molecular formula)

constitution: how are atoms connected/bonded (usually lewis structure)

configuration: how are bonds arranged in space (3D drawing)

conformation: what is the spatial relationships between bonds

Question 3

difference in structure between alkanes and alkenes:

Answer 3

alkanes are tetrahedral whilst alkenes are planar

Question 4

first ten names for organic skeletons:

Answer 4

meth-
ethe-
pro-
but-
pent-
hex-
hept-
oct-
non-
dec-

Question 5

isomer:

Answer 5

different compounds with the same molecular formula but have different bond constitution (different bond connectivity)

Question 6

isomers that differ in atom connectivity are either…

Answer 6

…. constitutional isomers or structural isomers

Question 7

what is the current molecule naming system called and what is it standardised by?

Answer 7

substitutive nomenclature which is standardised by the international union of pure and applied chemistry (IUPAC)

Question 8

if trying to name a branched hydrocarbon what must you do?

Answer 8

if branched, first identify the principle chain

Question 9

[naming] if two chains are equal in length…

Answer 9

… select the one with the most substituents

Question 10

when numbering the principle chain, give the lowest number to the…

Answer 10

… first branching point

Question 11

substituent:

Answer 11

a branching group from the principle chain

Question 12

how do you separate words and numbers when naming a molecule:

Answer 12

you always keep the words together but separate numbers using a hyphen

Question 13

order of naming in nomenclature:

Answer 13

number - substituent (s) - principle chain

Question 14

multiple of the same substituent:

Answer 14

methyl

dimethyl

trimethyl

Question 15

composition:

Answer 15

shows what elements are present and their amounts

Question 16

constitution:

Answer 16

shows connectivity - how atoms are connected or bonded

Question 17

configuration:

Answer 17

shows the three-dimensional arrangement of atoms in space

Question 18

dihedral angle:

Answer 18

also known as the torsional angle, rotation can occur along single bonds

Question 19

what is the speed of rotation like at single bonds?

Answer 19

rotation around single bonds is rapid except at very low temperatures

Question 20

what strain does Van De Walls repulsion create and what does it encourage?

Answer 20

Van De Walls repulsion causes torsional strain encouraging rotation towards a more stable conformer

Question 21

how do you assign formal charge?

Answer 21

identify the group and write down the number

then subtract the number of bonds

then subtract the number of lone electrons

Question 22

what are the two exceptions to the octet rule and how do they break the rule?

Answer 22

the two exceptions are carbon & boron which can actually form positive, electron deficient states