Lecture 2 - Chemistry of Alkanes Flashcards
two classes of hydrocarbons:
aliphatic and aromatic
define the 4 C’s
composition:
constitution:
configuration:
conformation:
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
difference in structure between alkanes and alkenes:
alkanes are tetrahedral whilst alkenes are planar
first ten names for organic skeletons:
meth-
ethe-
pro-
but-
pent-
hex-
hept-
oct-
non-
dec-
isomer:
different compounds with the same molecular formula but have different bond constitution (different bond connectivity)
isomers that differ in atom connectivity are either…
…. constitutional isomers or structural isomers
what is the current molecule naming system called and what is it standardised by?
substitutive nomenclature which is standardised by the international union of pure and applied chemistry (IUPAC)
if trying to name a branched hydrocarbon what must you do?
if branched, first identify the principle chain
[naming] if two chains are equal in length…
… select the one with the most substituents
when numbering the principle chain, give the lowest number to the…
… first branching point
substituent:
a branching group from the principle chain
how do you separate words and numbers when naming a molecule:
you always keep the words together but separate numbers using a hyphen
order of naming in nomenclature:
number - substituent (s) - principle chain
multiple of the same substituent:
methyl
dimethyl
trimethyl
composition:
shows what elements are present and their amounts
constitution:
shows connectivity - how atoms are connected or bonded
configuration:
shows the three-dimensional arrangement of atoms in space
dihedral angle:
also known as the torsional angle, rotation can occur along single bonds
what is the speed of rotation like at single bonds?
rotation around single bonds is rapid except at very low temperatures
what strain does Van De Walls repulsion create and what does it encourage?
Van De Walls repulsion causes torsional strain encouraging rotation towards a more stable conformer
how do you assign formal charge?
identify the group and write down the number
then subtract the number of bonds
then subtract the number of lone electrons
what are the two exceptions to the octet rule and how do they break the rule?
the two exceptions are carbon & boron which can actually form positive, electron deficient states