Module 4.2
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Give an overview of alcohols
• Aliphatic - General formula = CnH2n+1OH
Describe the polarity of alcohols
The electronegative oxygen from the OH (of the alcohol) draws electron density from hydrogen making it slightly positive (delta-positive). This slightly positive hydrogen can attract the lone pair of an oxygen from a neighbouring molecule (such as water) forming hydrogen bonds with it. Therefore, alcohols are polar.
What bonds to alcohols form with water? (and between what atoms)
Alcohols can form hydrogen bonds with water. Between H( (H must have a delta positive charge on it) and O (O must have a delta negative charge on it and a lone pair)
Explain in terms of hydrogen bonding, the solubility of alcohols compared with alkenes
• When you mix an alcohol, with water, hydrogen bonds are formed. If it’s a small alcohol, hydrogen bonding lets it mix freely with water. Therefore, small alcohols are soluble in water. However, in larger alcohols, most of the molecule is NON-POLAR. So there is less attraction for the polar water molecules. This means that as alcohols increase in size, their solubility decreases.
Explain in terms of hydrogen bonding, the relatively low volatility of alcohols compared with alkenes
Alcohols have a relatively low volatility because the hydrogen bonds require so much energy to break. Another saying for this is : Alcohols don’t evaporate easily to gas because the H bonds require so much energy to overcome.
What are the 3 types of alcohol?
Primary Secondary Tertiary
Define a primary alcohol
An organic compound, with an OH group, in which the OH group is at the end of a carbon chain.
Define a secondary alcohol
An organic compound, with an OH group, in which the OH group is attached to a carbon atom that is attached to 1 hydrogen
Define a tertiary alcohol
An organic compound, with an OH group, in which the OH group is attached to a carbon atom which is attached to no hydrogen groups
Give examples of a primary alcohols
Ethanol Butanol Hexanol Propan-1-ol Pentan-1-ol
Give examples of secondary alcohols
Propan-2-ol Butan-2-ol Hexan-2-ol Pentan-2-ol
Give examples of tertiary alcohols
2-methylpropan-2-ol 2-methylbutan-2-ol 3-methylpentan-3-ol
What are the products in the complete combustion of an alcohol?
Carbon Dioxide and Water
How do you balance the reaction between an alcohol and oxygen?
• First balance the hydrogen • Then balance the carbon • Lastly balance the oxygens
What does the sign [O] represent?
An oxidising agent
Describe the oxidation of primary alcohols to form aldehydes (Give the reagents, conditions, the observation, a generic equation and an example equation)
Regeants - Oxidising agent (Acidified Potassium Dichromate) = K2Cr2O7/H2SO4 Conditions = Distillation Generic = R-CH2-OH + [O] → R-CHO + H2O Example = CH3CH2OH + [O] → CH3CHO + H2O Colour change - Orange to Green
Describe the oxidation of primary alcohols to form carboxylic acids(Give the reagents, conditions, the observation, a generic equation and an example equation)
Regeants - Oxidising agent (Acidified Potassium Dichromate) = K2Cr2O7/H2SO4 Conditions = Reflux Generic = R-CH2-OH + 2[O] → R-COOH + H2O Example = CH3CH2OH + 2[O] → CH3COOH + H2O Colour change - Orange to Green
State the functional group and location of aldehydes
CHO Functional Group Location = End of the chain
What do aldehydes end in?
-al
State the functional group and location of carboxylic acids
COOH Functional Group Location = At the end of the chain
What do carboxylic acids end?
• oic acid
Describe the oxidation of secondary alcohols to form ketones Give the reagents, conditions, the observation, a generic equation and an example equation
Regeants - Oxidising agent (Acidified Potassium Dichromate) = K2Cr2O7/H2SO4 Conditions = Reflux Generic = R-CH(OH)-CH3 + [O] →R-C(O)-CH3 + H2O Example = CH3CH2CH3 + [O] → CH3COCH3 + H2O Colour change - Orange to Green
Describe the resistance of oxidation of tertiary alcohols
Tertiary alcohols cannot be oxidised using an oxidation agent such as acidified potassium dichromate because in order for oxidation to occur, the -OH must be attached to a carbon that has at least ONE hydrogen attached to it. For tertiary alcohols, this is not the case
Describe the dehydration of water from alcohols to form alkenes (Give the reagents and conditions)
Reaction name = Dehydration Regeants = CONC sulphuric acid OR CONC phosphoric acid Conditions = Reflux, 180 degrees celsius Products = Alkene + Water