WJEC A-Level Chemistry Organic Compounds Past Paper PDF

WJEC Okay, here are 20 multiple choice questions based on topic 2.4 Organic Compounds, focusing on naming and isomerism, as per the WJEC A Level Chemistry document provided: Questions: 1. What type of isomerism is shown by molecules with the same molecular formula but different structural formulae...

WJEC Okay, here are 20 multiple choice questions based on topic 2.4 Organic Compounds, focusing on naming and isomerism, as per the WJEC A Level Chemistry document provided: Questions: 1. What type of isomerism is shown by molecules with the same molecular formula but different structural formulae? * A) Stereoisomerism * B) Structural isomerism * C) Optical isomerism * D) E/Z isomerism 2. Which of the following describes chain isomers? * A) Same molecular formula, different functional group position. * B) Same molecular formula, different arrangement of the carbon chain. * C) Same structural formula, different spatial arrangement of atoms. * D) Same molecular formula, different functional group. 3. What is the term for isomers that have the same molecular formula, but the functional group is on a different position on the carbon chain? * A) Chain isomers * B) Position isomers * C) Functional group isomers * D) Stereoisomers 4. Which pair of compounds could be functional group isomers of each other? * A) Butane and 2-methylpropane * B) 1-chlorobutane and 2-chlorobutane * C) Cyclobutane and but-1-ene * D) But-1-ene and But-2-ene 5. E/Z isomerism is a type of: * A) Structural isomerism * B) Stereoisomerism * C) Chain isomerism * D) Functional group isomerism 6. What is the molecular formula of a compound? * A) Simplest ratio of atoms of each element in a compound * B) The total number of atoms of each element in a molecule of a compound. * C) The name of a compound based on it's functional groups. * D) The way in which the atoms in a compound are arranged 7. What is necessary for a molecule to exhibit E/Z isomerism? * A) A carbon chain of at least four carbon atoms. * B) A C=C double bond and two different groups attached to each carbon of the C=C. * C) A chiral centre. * D) At least one halogen atom. 8. In E/Z isomerism, what does the "Z" stand for? * A) The priority groups are on opposite sides of the double bond. * B) The priority groups are on the same side of the double bond. * C) The molecule contains a triple bond. * D) The molecule is a cyclic compound. 9. According to the Cahn-Ingold-Prelog (CIP) priority rules, which atom takes priority? * A) lowest atomic mass * B) lowest atomic number * C) highest atomic mass * D) Highest atomic number. 10. What is a nucleophile? * A) An electron-de cient species. * B) An electron-rich species and electron pair donor. * C) A species with a positive charge. * D) A species with an unpaired electron. 11. What is an electrophile? * A) An electron-de cient species and electron pair acceptor. * B) An electron-rich species. * C) A species with a negative charge. * D) a species that donates a pair of electrons 12. What does a curly arrow represent in a reaction mechanism? fi fi * A) The movement of a single electron. * B) The movement of a pair of electrons. * C) The breaking of a bond. * D) The formation of a free radical. 13. Which of these is the correct de nition for the term 'Addition'? * A) An atom/group that is exchanged in a molecule * B) An atom/group of atoms that is added to a molecule. * C) An atom/group that is removed from a molecule * D) an atom/group that accepts a pair of electrons. 14. What type of stereoisomerism is shown by butan-2-ol? * A) E/Z isomerism * B) Optical isomerism * C) Chain isomerism * D) Positional isomerism 15. What is the name given to a carbon atom with four different groups attached? * A) asymetrical carbon atom * B) Chiral carbon atom * C) Chiral centre * D) all of the above 16. Which of these is a correct de nition for an optical isomer? * A) A pair of non-superimposable mirror images. * B) Molecules with the same structural formula, but a different arrangement of atoms in space. * C) Molecules that rotate plane polarised light. * D) all of the above. 17. How many optical isomers does a molecule with one chiral centre have? * A) 1 * B) 2 * C) 3 * D) 4 18. What is a racemic mixture? * A) An equimolar mixture of two optical isomers. fi fi * B) A mixture containing one optical isomer. * C) A mixture of structural isomers. * D) A mixture that rotates plane-polarised light. 19. What effect does a racemic mixture have on plane-polarised light? * A) Rotates it clockwise. * B) Rotates it anticlockwise. * C) No overall effect. * D) Rotates in by +/_ 90 degrees. 20. What is the correct de nition of stereoisomers * A) molecules that have the same molecular formula but a different structural formula. * B) molecules that have the same molecular formula but a different arrangement of atoms in space. * C) molecules that have the same structural formula but a different arrangement of atoms in space. * D) Molecules that have the same structural formula, but the same arrangement of atoms in space. Answers and Explanations: 1. B) Structural isomerism - De nition of structural isomers. 2. B) Same molecular formula, different arrangement of the carbon chain. - De nition of chain isomers. 3. B) Position isomers - De nition of position isomers. 4. C) Cyclobutane and but-1-ene - Both have the molecular formula C4H8, but different functional groups. 5. B) Stereoisomerism - E/Z isomerism is a speci c type of stereoisomerism. 6. B) The total number of atoms of each element in a molecule of a compound. Correct de nition. 7. B) A C=C double bond and two different groups attached to each carbon of the C=C. - These are the requirements for E/Z isomerism. fi fi fi fi fi fi  8. B) The priority groups are on the same side of the double bond. - "Z" stands for "zusammen," meaning "together" in German. 9. D) Highest atomic number. - CIP rules prioritize based on atomic number. 10. B) An electron-rich species and electron pair donor. - De nition of a nucleophile. 11. A) An electron-de cient species and electron pair acceptor. - De nition of an electrophile. 12. B) The movement of a pair of electrons. - Curly arrows always represent the movement of a pair of electrons in mechanisms. 13. B) An atom/group of atoms that is added to a molecule. correct de nition. 14. B) Optical isomerism Butan-2-ol has a chiral centre 15. D) all of the above all options are correct 16. D) all of the above. All options are correct de nitions 17. B) 2 One chiral centre leads to two optical isomers (enantiomers). 18. A) An equimolar mixture of two optical isomers. - De nition of a racemic mixture. 19. C) No overall effect. - The rotations of the two enantiomers cancel each other out. 20. C) molecules that have the same structural formula but a different arrangement of atoms in space. Correct de nition according to the document provided. fi fi fi fi fi fi fi