How can alcohols be produced and what are their properties ? Flashcards
why are the boiling points of alcohols higher than their parent alkanes ?
because of the hydrogen bonding between alcohols molecules
why is the oxygen-hydrogen bond in a hydroxyl group polar?
because the oxygen is more electronegative than hydrogen
write out how hydrogen bonding occurs between the partially charged hydrogen atom and a non-bonding electron pair on the oxygen atom
reference pg 321
what does hydrogen bonding do to alcohols?
it gives them all relatively high boiling points
what is the effect of chain length on boiling point ?
as the length of the hydrocarbon chain increases, so does the dispersion forces and hence the size of the molecule increases. this also means that the boiling points of alcohols increase as molar mass increases.
in alcohols, what affects bond strength?
branching reduces the strength of dispersion forces and the position of the hydroxyl group affects hydrogen bonding.
write out isomers butan-1-ol, butan-2-ol and 2-methylpropan-2-ol and organise them in decreasing boiling points. why does this happen?
secondary and tertiary alcohols have lower boiling points than primary alcohols because hydrogen bonding is weaker in secondary and tertiary alcohols.
how does ethanol dissolve in water? draw a diagram of this
because it is a short hydrocarbon, it dissolves well in water by forming hydrogen bonds between the partially positive hydrogen atom of the hydroxyl and the lone-pair electrons from the water molecule.
what is the trend of solubility and chain length of alcohols in water?
the solubility of alcohol in water decreases as the hydrocarbon chain of the molecule becomes longer
what happens to the bonding when chain length increases?
the longer hydrocarbon chain disrupts the hydrogen bonds between water molecules.
why does solubility of alcohols in water decrease when the chain increases? (refer to bonding)
the only part of the alcohol molecule that can form hydrogen bonding is the hydroxyl group between water molecules, the rest of the hydrocarbon cannot. only dispersion forces occur between the hydrocarbon chain and water molecules, which are not as strong as hydrogen bonds. this means that when the chain increases, the non-polar nature of the molecule also increases and the alcohol becomes less soluble.
what is the trend of solubility of alcohols in organic solvents?
alcohols become more soluble in organic solvents as their molecules become larger.
why do longer alcohols dissolve better with organic solvents?
because organic solvents are non-polar, and only relatively non-polar alcohols with long chains dissolve well in non-polar solvents.
why don’t smaller alcohols (like ethanol) dissolve well in non-polar solvents?
since the chain is small and hydrogen bonding is stronger than dispersion forces, the dispersion forces between the hydrocarbon chain and the solvent molecules are overpowered and not strong enough to disrupt the hydrogen bonding that holds the alcohol molecules together. therefore, the alcohol molecules don’t mix with the solvent.
