Alcohols Flashcards
What is the general formula of an alcohol?
CnH2n+1OH
What is the functional group of an alcohol?
-OH hydroxl
Why may an alcohol be polar?
The hydroxyl bond is polar as the oxygen is more electronegative.
Why are alcohols soluble in water?
Alcohols interact with water molecules via a hydrogen bond. This is because the delta positive hydrogen on a water molecule is attracted to the lone pair of electrons on the oxygen of an alcohol. This allows alcohols to dissolve in water.
Why are longer carbon chained alcohols have a lower boiling point than shorter chained ones?
A carbon chain is non-polar and a longer carbon chain reduces the interaction water can make with an alcohol.
Alcohols have higher boiling points than other molecules of a similar relative mass. Why is this?
Alcohol molecules are able to form hydrogen bonds with each other. Hydrogen bonds are the strongest type of intermolecular force, so more energy is needed to break it. This gives a higher boiling point.
How to make a haloalkane from an alcohol?
React the alcohol with a halide ion (NaCl, LiBr…). This is a substitution reaction so the hydroxyl group will swap out for the halide ion. This reaction must be done under the condition of an acid catalyst like H2SO4.
For example, if propan-2-ol reacted with NaCl, the products would be 2-chloropropane and NaOH. This would be done with an acid catalyst.
How to form an alkene from an alcohol?
This happens via a dehydration reaction. This dehydration reaction is also an elimination reaction, as an alcohol forms an alkene and a water molecule. There are two possible alkene products that can be formed.
What are the conditions for the dehydration of an alcohol?
Heat, and an acid catalyst like phosphoric acid.
One way of oxidising an alcohol happens via the combustion. What are the reagents and products?
Alcohol + oxygen > carbon dioxide + water
How to form an aldehyde from a primary alcohol?
React primary alcohol with oxidising agent, acidified potassium dichromate, under distillation conditions. This is only partial oxidation. Solution turns from orange to green. Water is formed.
How to form a carboxylic acid from a primary alcohol?
React primary alcohol with oxidising agent, acidified potassium dichromate, under reflux conditions. This is complete oxidation. Solution turns from orange to green. Water is formed.
Why must the oxidation of a primary alcohol be done under distillation conditions if we are aiming to obtain an aldehyde?
Once the aldehyde is formed, distilling it immediately prevents it from oxidising further into a carboxylic acid.
State the features of reflux conditions. What are the advantages of reflux?
In reflux, the condenser tube is placed upright, and the top end of the condenser is open. Reflux is advantageous as it allows a reaction to continue without any product escaping (by boiling, then condensing the gas so it falls back down). Reflux also increases the rate of reaction if the mixture is constantly being heated.
How to obtain a ketone from a secondary alcohol?
React the secondary alcohol with acidified potassium dichromate, under reflux conditions.
