Organic synthesis and reaction pathwaysEdexcel A-Level Chemistry: Flashcards

Exam questions on Organic synthesis and reaction pathways

1. An organic liquid X contains only carbon, hydrogen and oxygen. Complete combustion of 0.296 g of X gives 0.704 g of carbon dioxide and 0.360 g of water. The mass spectrum of X has its molecular ion peak at m/z = 74. The infrared spectrum of X has a broad absorption at about 3300 cm⁻¹ and no absorption near 1700 cm⁻¹. Relative atomic masses: H = 1.0, C = 12.0, O = 16.0.
   The ¹H NMR spectrum of X has two singlets with relative peak areas 9 : 1, and X is not oxidised by warm acidified potassium dichromate(VI). Deduce the structural formula of X and explain how the data support your answer.2 marks
2. Grignard reagents are made by reacting a bromoalkane with magnesium. Ethylmagnesium bromide, CH₃CH₂MgBr, is made from bromoethane and is then used to lengthen carbon chains.
   CH₃CH₂MgBr reacts with propanone, and dilute acid is then added. Give the structural formula of the organic product and explain why the Grignard reagent attacks the carbonyl carbon.2 marks
3. Chemists often need to lengthen a carbon chain by one carbon atom. Butanoic acid can be made from propan-1-ol by a route using a nitrile or by a route using a Grignard reagent. Hazard data: potassium cyanide is toxic if swallowed or in contact with skin and releases toxic hydrogen cyanide gas with acids; diethyl ether is extremely flammable (flash point −45 °C) and can form explosive peroxides; Grignard reagents react violently with water.
   Suggest a three-step route from propan-1-ol to butanoic acid using a nitrile. Give the reagents and conditions for each step.3 marks