introduction to organic chemistry & alkanes Flashcards
What are alkanes
Saturated hydrocarbons
What is the general formula for an alkane
CnH2n + 2
What is the general formula for an alkene and a cycloalkane
CnH2n
State two features of a homologous series
• each member differs from the next member by the addition of a -CH2- ‘unit’.
• a general formula can be written for the series, e.g. for an alkane this is CH2n+2.
• members of a homologous series have very similar chemical properties
• they have the same functional group.
• members will show a change in physical properties like increasing boiling point as the carbon chain gets longer.
What is positional isomerism
Position of functional group is different
What is chain isomerism
Length of carbon chain is different
What is functional group isomerism
Functional group is different
To have E/Z isomerism a molecule must have
No rotation around Caron = Carbon double bond
Both C atoms in C=C bond must be bonded to different groups
Define hydrocarbons
Are compounds containing carbon and hydrogen only
Define saturated
Compounds contain single bonds only
The boiling point increases with increasing carbon chain length in terms of these intermolecular forces
Because
Longer chain = bigger molecule = more E-s
= stringer induced dipole dipole attractions between molecules
When the amount of branching increases, the number of electrons stays the same, the boiling point decreases
This is because
Branches molecules have less surface contract between molecules
So weaker induced dipole dipole attractions between molecules
Name a process of separating an alkane from a mixture of compounds :
Fractional distillation
What is the process of fractional distillation
The crude oil is passed into a tall tower called a fractionating column.
This is very hot near the base but much cooler near the top.
When the crude oil is passed into the tower, near the bottom, most of the mixture boils and starts to rise up the tower by a series of trays containing bubble caps. As they rise up the tower, they start to cool down and will gradually condense back into liquid form at a tray which is at a slightly lower temperature than their boiling point.
The liquids that condense at that tray are then piped off.
The larger hydrocarbons, with higher boiling points, will condense first and be piped off near the base of the column.
The smaller hydrocarbons, with smaller boiling points, will condense later and be piped off near the top of the column.
This process involves breaking intermolecular forces only; the molecules themselves are unaffected by this process
Define fractions
Mixture of hydrocarbons with similar boiling points
