Older MCQs might not have the typical A, B, C,
D
choices. They
have choices 1, 2, 3, and a combination of them is the answer. Below is the key that maps such
combinations to the answer.
A
1, 2 and 3 are correct
B
1 and 2 only are correct
C
2 and 3 only are correct
D
1 only is correct
recall the reactions (reagents and conditions) by which halogenoalkanes can be produced: (a) the free-radical substitution of alkanes by \( Cl_2 \) or \( Br_2 \) in the presence of ultraviolet light, as exemplified by the reactions of ethane (b) electrophilic addition of an alkene with a halogen, \( X_2 \), or hydrogen halide, \( HX(g) \), at room temperature (c) substitution of an alcohol, e.g. by reaction with \( HX(g) \); or with KCl and concentrated \( H_2SO_4 \) or concentrated \( H_3PO_4 \); or with \( PCl_3 \) and heat; or with \( PCl_5 \); or with \( SOCI_2 \)
recall the reactions (including reagents and conditions) by which alkenes can be produced: (a) elimination of HX from a halogenoalkane by ethanolic NaOH and heat (b) dehydration of an alcohol, by using a heated catalyst (e.g. \( Al_2O_3 \)) or a concentrated acid (e.g. concentrated \( H_2SO_4 \)) (c) cracking of a longer chain alkane
