How many sigma and pi bonds in
a) single bonds
b) double bonds
c) triple bonds
a) single = 1 sigma bond
b) double = 1 sigma bond, 1 pi bond
c) triple = 1 sigma bond, 2 pi bonds
What is the general molecular formula for ALKANES
C(n)+H(2n+2)
How to name branched alkanes:
- Find the longest carbon chain (if 2 of equal size are present, choose the one with the larger number of branch points as the primary)
- number C atoms in main chain, begin at end nearest 1st branch point
- Assign a number to each substituent according to which C it is attached to (you can assign the same number twice)
Use hyphens to separate numbers from words, and commas to separate numbers from numbers. Put them in alphabetical order. (don’t consider di, tri, tetra, prefixes when alphabetising)
General formula for cycloalkanes
C(n)H(2n)
Naming alkenes and alkynes
- Find parent hydrocarbon (longest chain with double or triple bond) use the suffix -ene for alkenes and -yne for alkynes
- Number parent hydrocarbon, start at the end nearest C-C double or triple bond
- Number substituents, list alphabetically
- Indicate the position of double or triple bond by giving the number of 1st alkene/alkyne C atom, place number before suffix
- Account for multiple double or triple bonds if more than one, use suffixes
Where to number cycloalkene double bond?
Between C1 and C2
How to name cycloalkanes?
- Count number of C atoms and add prefix cyclo- to the name of the corresponding alkane, if substituents are present, the compound is named as an alkyl-substituted cycloalkane
- For substituted cycloalkanes, start at a point of attachment and number around the ring. If 2 or more substituents are present, start numbering at the group with alphabetical priority and proceed around
what is a constitutional isomer?
Same molecular formula, bonded differently
When is it appropriate to use the prefix ‘iso’?
often given to alkanes isomers with a methyl group attached to the 2nd C in the chain
List some physical properties of alkanes and explain why these properties occur.
- Physical properties of alkanes occur due to their lack of polarity in C-H & C-C bonds
- Boiling and melting point increase with molar mass and number of atoms
- Weak intermolecular forces of alkanes = low boiling point
- alkenes and alkynes are soluble in each other but are immiscible in water as they are non-polar
Explain the difference in physical properties of isomeric alkanes
The least branched isomer has the highest BP - more surface area and an increase in dispersion forces
The most branched isomer has the lowest BP - smaller surface area and a decrease in dispersion forces
Why do alkanes have limited reactivity?
Because they are saturated (H at every possible bonding site on the C atom)
What is an addition reaction of alkenes?
Molecules of 2 reactants add together to form a single new product
The most common reaction of alkenes invokes the addition across the double bond to produce saturated (single bonded) compounds
What is hydrohalogenation of alkenes and alkynes?
The addition of hydrogen halides (HCl, HBr, HI) to alkenes/alkynes to produce haloalkanes/alkynes (alkyl halides)
What is halogenation of alkanes?
Alkanes react with chlorine or bromine at high temps or in the presence of light to give alkyl chlorides/bromides
What is hydration of alkenes?
The addition of water to alkenes
Alkenes react with H2 in the presence of a transition metal catalyst to yield alkanes
also called catalytic reduction/hydrogenation
What is the polymerisation of alkenes?
In addition polymerisation (aka chain-growth polymerisation), a chain reaction adds new monomer units to the growing polymer molecule one at a time through double or triple bonds in the monomer
What happens in the combustion reaction of alkanes?
Alkanes burn in the presence of oxygen, CO2 and H2O are formed as products and large amount of heat is released
