Photochemistry (Paper II) – Chemistry Optional PYQs (2000–2026)

Here are all 64 Photochemistry (Paper II) questions asked in UPSC Chemistry Optional Paper II from 2000 to 2026, with the latest questions first.

Each question ends with a code such as [2024/15m/3b] – the year, the marks, the word limit (where UPSC set one) and the question number in the paper.

64 questions

1. Write the structures of the major products M, N, O and P in the following reaction sequence. Suggest a mechanism for the conversion of O to P.

[Figure: Scheme: 2,6-dimethylphenol (OH at top, CH3 on both ortho carbons) –(i) K2CO3; (ii) CH3COCl (arrow to the left)→ M –hν (downward)→ N; 2,6-dimethylphenol –(i) NaH; (ii) (E)-1-bromoprop-1-ene (H3C–CH=CH–Br, CH3 and Br trans) (arrow to the right)→ O –Δ, 220°C (downward)→ P] [2026/15m/3b]

2. Explain why 2-methyl benzophenone undergoes rapid and reversible photo-enolisation reaction. Discuss the stereoisomerism of the photo-enol formed. [2026/10m/5c]

3. What are the phenomena that result in the emission wavelength being longer than the excitation wavelength in photochemical reactions? [2026/5m/7a(i)]

4. Why is phosphorescence slower than fluorescence? Explain. [2026/5m/7a(ii)]

5. Complete the following Norrish Type I reaction: $C_6{H}_5-CH\left(C_6{H}_5\right)-CO-CH\left(C_6{H}_{4}C{H}_3\left(4\right)\right)-C_6{H}_{4}C{H}_3\left(4\right)\stackrel{h\nu }{\to }$ [2026/10m/7b(i)]

6. Do Norrish Type II reactions proceed through singlet state and/or triplet state? Justify your answer with two different examples. [2026/10m/7b(ii)]

7. A photochemical reaction takes place through $T_1$ state. $S_0$–$S_1$ and $S_0$–$T_1$ energy gaps correspond to 290 nm and 450 nm, respectively. To get an efficient photochemical reaction should we use light of 290 nm or 450 nm? Give your answer presenting the relevant Jablonski diagram. [2025/10m/5c]

8. Write the mechanism for the following photochemical transformation:

[Figure: Reaction: benzene –hν→ fulvene (5-methylenecyclopenta-1,3-diene)] [2025/5m/6c(i)]

9. Photobromination of cinnamic acid was carried out by using light of wavelength 480 nm with a light intensity of $1.5\times {10}^{-3}J\mathrm{\text{–}}{s}^{-1}$. An exposure of 10 minutes showed a decrease of 0.05 millimole of $B{r}_2$. Calculate the quantum yield assuming that 80% of radiation is absorbed by cinnamic acid. (Planck’s constant $h=6.627\times {10}^{-34}$ J-s and velocity of light $c=3\times {10}^{8}m\mathrm{\text{–}}{s}^{-1}$) [2025/5m/6c(ii)]

10. Predict the major and minor products for the following photoreaction. Give the logic:

[Figure: Reaction: 4,5-dimethylhexan-2-one, CH3–CO–CH2–CH(CH3)–CH(CH3)–CH3 (drawn as CH3–CH(CH3)–CH(CH3)–CH2–C(=O)–CH3) –hν→ ?] [2025/5m/6c(iii)]

11. Assign A, B and C in the following reaction:

[Figure: Reaction: Ph2CH–CO–CHPh2 + PhCH2–CO–CH2Ph –hν (vertical arrow)→ A + B + C (Major) + CO] [2025/5m/6c(iv)]

12. Write down the product(s) in the following reactions: (i) $C_6{H}_{5}COCOO{C}_2{H}_5+C{H}_{3}CHOH{C}_2{H}_5\stackrel{h\nu }{\to }$ (ii) $C{H}_{3}COCOO{C}_2{H}_5+C{H}_{3}OH\stackrel{h\nu }{\to }$ [2024/10m/5c]

13. Write down the mechanism for the formation of compounds B and C from compound A on photoirradiation:

[Figure: A: bicyclo[5.3.0] (hydroazulene) ketol: cyclopentanone fused to a cycloheptane; one ring-fusion carbon bears OH, the other (adjacent to C=O) bears CH3; the cycloheptane carbon next to the C–OH carbon bears CH3. B: spiro γ-lactone: a five-membered lactone (O–C(=O)–CH2–CH2–) spiro-fused at the carbon bearing the ring O to a cycloheptane that carries CH3 on both carbons adjacent to the spiro carbon. C: spiro lactol: the corresponding five-membered cyclic hemiacetal (ring CH bearing OH next to the ring O) spiro-fused to a cycloheptane bearing CH3 on one adjacent carbon and an exocyclic =CH2 on the other adjacent carbon] [2024/15m/6b]

14. Ethanolic solution of compound I on irradiation leads to the formation of compounds II, III and IV. The resulting reaction mixture exhibits bands at 1787, 1740, 1715 and $1685c{m}^{-1}$ for ${\nu }_{C=O}$. Assign these C=O stretching frequencies to the corresponding compounds giving reasons:

[Figure: Reaction: I (verbenone: 4,6,6-trimethylbicyclo[3.1.1]hept-3-en-2-one, α,β-unsaturated bicyclic ketone with the gem-dimethyl bridge) –hν, EtOH→ II (chrysanthenone: isomeric bicyclo[3.1.1] ketone with the C=O on the four-membered ring and the C=C(CH3) in the six-membered ring) + III (ethyl 3,7-dimethylocta-2,6-dienoate, (CH3)2C=CH–CH2–CH2–C(CH3)=CH–COOEt) + IV (ethyl 3,7-dimethylocta-3,6-dienoate, (CH3)2C=CH–CH2–CH=C(CH3)–CH2–COOEt)] [2024/15m/8a]

15. Identify the products in the above reactions with plausible mechanism.

[Figure: (i) $C{H}_3\mathrm{\text{–}}CO\mathrm{\text{–}}C{H}_3\underset{\mathrm{\text{Vapour phase}}}{\stackrel{h\nu }{\to }}$ ; (ii) $C{H}_3\mathrm{\text{–}}CO\mathrm{\text{–}}C{H}_3\underset{\mathrm{\text{Room temperature}}}{\stackrel{h\nu }{\to }}$ (acetone drawn as CH3–C(=O)–CH3)] [2023/10m/5e]

16. Identify all the possible products in the above reaction showing the sequential pathways of their formation:

[Figure: Reaction: cyclopentanone –hν, Vapour phase→] [2023/10m/7b(i)]

17. 1,3-Butadiene solution on irradiation with UV light follows path I. However, irradiating 1,3-butadiene in the presence of benzophenone at 366 nm follows path II. Give a suitable explanation.

[Figure: Scheme: buta-1,3-diene –hν (Path I)→ cyclobutene + bicyclo[1.1.0]butane; buta-1,3-diene –${\left(C_6{H}_5\right)}_{2}CO$, 366 nm (Path II)→ 1,2-divinylcyclobutane + 4-vinylcyclohexene] [2023/5m/7b(ii)]

18. Considering the structural features of ergosterol ($A$) and precalciferol ($B$), a precursor of vitamin D, giving mechanistic details, explain why vitamin D deficiency is endemic in those parts of the world where sunlight is scarce:

[Figure: $A$ = ergosterol: steroid skeleton with 3β-OH (HO on wedge), C-19 methyl on a wedge at C-10, 9α-H (hashed), conjugated C5=C6 and C7=C8 double bonds in ring B, C-18 methyl at C-13, side chain at C-17 $CH\left(C{H}_3\right)\mathrm{\text{–}}CH=CH\mathrm{\text{–}}CH\left(C{H}_3\right)\mathrm{\text{–}}CH{\left(C{H}_3\right)}_2$; $B$ = precalciferol (previtamin D2): ring B opened between C-9 and C-10, ring A bearing HO (wedge) and a methyl on the C-10 double bond carbon (C5=C10), a cis C6=C7 linkage, and C8=C9 in ring C, with the same C-17 side chain and C-18 methyl] [2022/10m/3b(i)]

19. Write down the products obtained after photolysis of 2-methylcyclohexanone in solution phase. Explain the formation of products. [2022/10m/5b]

20. Predict the products in the following reactions: (i) Propose suitable mechanism to justify your answer. (ii) Giving justification, write the major and minor product(s). Comment upon the chirality of recovered reactant (if any).

[Figure: (i) 1-phenylpentan-1-one (Ph–CO–CH2CH2CH2CH3) + 5,5-dideuteriohexan-2-one ($C{H}_3\mathrm{\text{–}}CO\mathrm{\text{–}}C{H}_2\mathrm{\text{–}}C{H}_2\mathrm{\text{–}}C{D}_2\mathrm{\text{–}}C{H}_3$) –hν→ ; (ii) 4,5-dimethylheptan-2-one ($C{H}_3\mathrm{\text{–}}CO\mathrm{\text{–}}C{H}_2\mathrm{\text{–}}CH\left(C{H}_3\right)\mathrm{\text{–}}CH\left(C{H}_3\right)\mathrm{\text{–}}C{H}_2\mathrm{\text{–}}C{H}_3$, no stereochemistry shown) –hν→] [2022/15m/6a]

21. Arrange the compounds in the above groups for ease of Norrish type-II H-abstraction in decreasing order giving the plausible explanations.

(i) I $Ph\mathrm{\text{–}}CO\mathrm{\text{–}}C{H}_{2}C{H}_{2}C{H}_3$; II $Ph\mathrm{\text{–}}CO\mathrm{\text{–}}C{H}_{2}C{H}_{2}C{H}_{2}C{H}_3$; III $Ph\mathrm{\text{–}}CO\mathrm{\text{–}}C{H}_{2}C{H}_2\mathrm{\text{–}}CH{\left(C{H}_3\right)}_2$ [2021/5m/5d(i)]

(ii) I $Ph\mathrm{\text{–}}CO\mathrm{\text{–}}C{H}_{2}C{H}_{2}C{H}_3$; II and III as drawn:

[Figure: II = 2-propyl-3,4-dihydronaphthalen-1(2H)-one (1-tetralone bearing $C{H}_{2}C{H}_{2}C{H}_3$ on C-2); III = 2-benzoylbicyclo[2.2.1]heptane (norbornane with COPh on C-2, drawn pointing down, away from the one-carbon bridge)] [2021/5m/5d(ii)]

22. Complete the above reactions by giving the suitable mechanisms.

(i) I. 2-cyclopropylcyclohexan-1-one –hν→ ? [2021/5m/6c(i)]

(ii) II. 1,3,3-triphenylpropan-2-one ($PhC{H}_2\mathrm{\text{–}}CO\mathrm{\text{–}}CHP{h}_2$) –hν→ ? [2021/10m/6c(ii)]

23. Complete the following reaction giving the structures of intermediates involved:

[Figure: Reaction: 2-methyl-2-[3-(4-methoxy-2-methylphenyl)-3-oxopropyl]-3-vinylcyclopentan-1-one (aryl ketone Ar–C(=O)–CH2–CH2– attached to the quaternary C2 of cyclopentanone, C2 bearing a CH3 on a wedged bond, C3 bearing a vinyl group; aryl = 4-methoxy-2-methylphenyl, MeO para and CH3 ortho to the ketone) –$h\nu$ (λ > 340 nm), Py, (Mesitol)→ ?] [2020/10m/5c]

24. Describe the steps involved in the following reaction:

[Figure: Reaction: cyclobutanone –1) $h\nu$; 2) ROH→ 2-alkoxytetrahydrofuran (tetrahydrofuran ring with OR on the carbon adjacent to ring O)] [2020/15m/6a]

25. Identify ($X$) and ($Y$) in the following reaction. Name the type of photochemical reaction involved:

[Figure: Reaction: bicyclo[2.2.1]hept-5-en-2-one (norbornenone) –$h\nu$→ ($X$) –$h\nu$→ ($Y$) + $C{H}_2=C=O$] [2019/10m/5c]

26. Identify ($X$) and ($Y$) in the following reaction:

[Figure: Reaction: 1,3-diphenyl-2-indanone (1,3-diphenyl-1,3-dihydro-2H-inden-2-one: benzene ring fused to a five-membered ring whose C1 and C3 each carry Ph and C2 is C=O) –$h\nu$→ ($X$) –maleic anhydride (drawn above the arrow), Δ→ ($Y$)] [2019/10m/8c(ii)]

27. Explain the conditions for the following reaction, very briefly describe the steps involved and comment if the reaction is reversible:

[Figure: Reaction: methyl vinyl ketone (but-3-en-2-one) + ethylene → 1-cyclobutylethan-1-one (methyl cyclobutyl ketone)] [2018/10m/1e]

28. Distinguish between fluorescence emission and phosphorescence emission giving suitable examples. [2018/10m/8a]

29. The direct irradiation of either cis- or trans-stilbene at 313 nm results in the formation of a mixture of 93% cis- and 7% trans-olefin, no matter how long, within reason, the irradiation is continued. Give a suitable explanation for that. [2018/10m/8b]

30. Classify the following reaction and propose a suitable mechanism for it:

[Figure: Reaction: cyclodecanone, drawn as a ten-membered ring in a naphthalene-like (two-hexagon) outline with the C=O carbon at the top centre and its O pointing into the middle of the ring –$h\nu$→ decahydronaphthalen-4a-ol (decalin with OH at the upper ring-fusion carbon and H, on a bold bond, at the lower ring-fusion carbon)] [2018/10m/8c]

31. Write the products for the following reactions.

[Figure: (i) 1,3-butadiene –hν→ branching to S1 → ? and T1 → ?; (ii) butan-2-one (CH3–CO–CH2CH3) –hν→ branching to Norrish type I → ? and Norrish type II → ?] [2017/10m/6c]

32. Compounds $A$ and $B$ undergo photodecarbonylation resulting in the formation of $I$ and $II$ (From $A$) and $III$ and $IV$ (From $B$). Give their structures.

[Figure: A = bicyclo[2.2.1]heptan-2-one (norcamphor) –hν→ CO + I + II; B = bicyclo[3.2.0]heptan-3-one (cyclobutane fused to cyclopentanone, C=O at the carbon remote from the ring fusion) –hν→ CO + III + IV] [2017/10m/6d]

33. Write the intermediates and possible products in the following photochemical reaction.

[Figure: Reaction: acetone (H3C–CO–CH3) + vinyl ether (CH2=CH–O–R) –hν→ ?] [2017/5m/7a(i)]

34. Among the following, identify the compound which can undergo Norrish type II reaction. Write the mechanism: (i) $C{H}_{3}COC{H}_{2}C{H}_3$ (ii) $C{H}_{3}COC{H}_{2}C{H}_{2}CH{\left(C{H}_3\right)}_2$ (iii) $C{H}_{3}COC{H}_{2}C{H}_{2}C{\left(C{H}_3\right)}_3$ (iv) $C_6{H}_{5}COC{H}_{2}C{H}_3$ [2016/10m/6a]

35. Write the intermediate and possible products for the following reaction:

[Figure: Reaction: cyclobutanone –hν, 325 nm→ ?] [2016/10m/6b]

36. Show Norrish type-II fragmentation for the following compound:

[Figure: 5-(furan-2-yl)-1-phenylpentan-1-one: C6H5–CO–CH2–CH2–CH2–CH2–(furan-2-yl)] [2015/10m/5c]

37. Suggest the product and offer the mechanism in the following reaction:

[Figure: Reaction: cyclohex-2-en-1-one –hν→ ?] [2015/10m/8b]

38. What is cis-trans photoisomerization? Give mechanism involved in the isomerizations of alkenes. Predict the equilibrium product in the following reaction:

[Figure: Reaction: cis-cyclononene drawn as a nine-membered ring with atoms numbered 1–9 and the C=C between C-1 and C-2 –hν (equilibrium arrows ⇌)→ ?] [2014/10m/5b]

39. Give mechanism involved in Norrish type II reaction and predict the products in the following reactions:

[Figure: Reaction: 2-(2-phenylethyl)-3,4-dihydronaphthalen-1(2H)-one (1-tetralone with a CH2CH2Ph group on C-2, the carbon α to the C=O) –hν→ ?] [2014/10m/8c]

40. Write the products of the following reactions and give the suitable mechanism:

[Figure: (i) 2-cyclopropylcyclohexanone: cyclohexanone with a cyclopropyl group on the carbon α to the C=O, arrow hν over, NS-I under; (ii) cyclodecanone drawn as a ten-membered ring folded into two hexagon-like halves sharing the C=O carbon (top) and the transannular carbon C-6 (bottom): the C=O oxygen points into the ring towards C-6, whose two H atoms are drawn one hashed and one wedged; arrow hν over, NS-II under] [2013/10m/3c]

41. (i) [structure] is exposed to u – v light and compounds C and D are produced. What are the structures of C and D? (ii) 1,3-butadiene is treated with $S{O}_2$. What product will be formed?

[Figure: The structure in (i): 5-methylcyclopent-2-en-1-one – cyclopentenone ring with C=O, a ring C=C conjugated with it, and a Me group on the ring carbon on the other side of the C=O] [2012/12m/1b]

42. (i) When compound A is treated with alkali what product is formed? Show the mechanism of the conversion.

[Figure: A = cyclodecane-1,6-dione: ten-membered carbocyclic ring with two C=O groups on opposite carbons (1 and 6)]

(ii) What is the structure of the compound produced from B on exposure with u – v light? $B=Ar-CH\left(Ar\right)-C(=O)-Ar$, Ar = 2,4,6-trimethyl phenyl

[Figure: B drawn as Ar – CH – C – Ar with a second Ar on the CH (bond drawn downwards) and =O on the C (drawn downwards), i.e. 1,2,2-triaryl-ethanone, Ar = mesityl] [2012/12m/1d]

43. (i) 1,4-butadiene carrying alkyl or aryl substitution on C-3, can photochemically rearrange to vinyl cyclopropane.

[Figure: Reaction scheme: 3,3-dialkyl-1,4-pentadiene (CH2=CH–CR2–CH=CH2, the central carbon bearing R and R) –hν→ 1,1-di-R-2-vinylcyclopropane (cyclopropane with a vinyl group on one ring carbon and two R groups on an adjacent ring carbon)]

Explain the transformation. (ii) What are the structures of pyrimidine nucleotides present in DNA? What are the structures of their purine conjugates? [2012/12m/5d]

44. Give the structure of (A) and its conversion to (B) with mechanism for the following transformation:

[Figure: bicyclo[2.2.1]hepta-2,5-dien-7-one (norbornadienone; C7 bridge carbon is C=O) [labelled (A) under the drawing] –(hν)→ (A) –(Δ)→ (B) tropone (cyclohepta-2,4,6-trien-1-one)] [2011/10m/5a]

45. How would you explain the transformation of butadiene to (A) and (B) by one route but (C), (D) and (E) as shown by a different route? Give the mechanism for the transformation.

[Figure: 1,3-butadiene –(hν, sens.)→ (C) trans-1,2-divinylcyclobutane + (D) cis-1,2-divinylcyclobutane + (E) 4-vinylcyclohexene; 1,3-butadiene –(hν, direct, downward arrow)→ (A) bicyclo[1.1.0]butane + (B) cyclobutene] [2011/20m/6b]

46. “Photo reaction of acetone with (A) by $S_1$ ($n\to {\pi }^{*}$) process gives cis and trans products, but with (B) gives only one isomer.” Explain.

[Figure: ${\left(C{H}_3\right)}_{2}C=O$ + (A) cis-1,2-dicyanoethylene (NC–CH=CH–CN, cis) → 2,2-dimethyloxetane-3,4-dicarbonitrile drawn twice: one isomer with plain bonds to both CN groups + one isomer with CN on C4 wedged and CN on C3 hashed; ${\left(C{H}_3\right)}_{2}C=O$ + (B) $C{H}_2=C\left(C{H}_3\right)CN$ (methacrylonitrile), downward arrow → single oxetane: ring O bonded to a carbon bearing $C{H}_3$ and CN and to a carbon bearing two $C{H}_3$, the fourth ring atom a $C{H}_2$ (2,4,4-trimethyloxetane-2-carbonitrile)] [2011/10m/7b(ii)]

47. Predict the products and explain their formation.

[Figure: norbornene (bicyclo[2.2.1]hept-2-ene) in the centre; to the left: –($C_6{H}_{5}CO{C}_6{H}_5$, hν)→ B; to the right: –($C{H}_{3}COC{H}_3$, hν)→ A] [2010/10m/5c]

48. Write the structures of possible products of following photochemical reactions and mention the type of Norrish process (I or II) in each.

[Figure: (i) 2-methylcyclohexanone –(hν)→ ; (ii) $C{H}_{3}C{H}_2-CO-C{H}_{2}C{H}_{2}CH\left(C{H}_3\right)C{H}_3$ (drawn as $C{H}_{3}C{H}_2-C(=O)-C{H}_{2}C{H}_{2}CHC{H}_3$ with a $C{H}_3$ hanging from the CH, i.e. 6-methylheptan-3-one) –(hν)→ ] [2010/15m/7a]

49. Photochemical (2 + 2) addition of benzophenone with cis- and trans-2-butene yield a mixture of same products. Explain their formation with the mechanism. [2010/15m/7b]

50. (i) Write products for photochemical dissociation of 2-pentanone. Write the possible intermediate. Identify A and B (ii) Write products of photochemical oxidation of following:

[Figure: (i) N-chloro-N-methylpentylamine drawn in a pseudo-ring (chair-like) conformation: N bearing Cl and $C{H}_3$ attached to a five-carbon chain whose terminal (δ) carbon, drawn next to N without a bond, carries the H shown –($H^{+}$, hν)→ A –(NaOH)→ B; (ii) (E)-4-methylpent-2-ene ($C{H}_3-CH=CH-CH{\left(C{H}_3\right)}_2$, the tertiary allylic H drawn explicitly) and anthracene] [2009/20m/6a]

51. What are Norrish type I and II photo-cleavages? [2008/20m/5a(ii)]

52. Identify A-D in the following.

[Figure: Scheme: cyclopentanone (five-membered ring =O) –hν→ [A] –(−CO)→ B → C, with B also giving $2C{H}_2=C{H}_2$ (vertical line from B to “2CH2=CH2”); [A] –γ-H abstraction (downward arrow)→ D] [2008/20m/6a]

53. Identify A-D in the following What are products formed by photodimerization of cyclopent-2-en-1-one? [2008/10m/6b]

54. (i) Explain the difference between singlet and triplet states of 1, 3-butadiene. (ii) Photolysis of ethyl methyl ketone gives biacetyl and n-butane whereas that of butyrophenone gives acetophenone and ethylene as products Explain. [2007/20m/7a]

55. Write the mechanism of the following reactions: (i) [see figure] (ii) [see figure] (iii) Dehydrobromination of meso and racemic 1, 2-dibromo-1, 2-diphenylethane given cis and trans 1-bromo-1, 2-diphenylethene respectively.

[Figure: (i) a trimethylcycloheptatriene with a gem-dimethyl ($H_{3}C$, $C{H}_3$) on the sp3 ring carbon and a further $H_{3}C$ on a ring double-bond carbon –hν→ an isomeric trimethylcycloheptatriene (one $C{H}_3$ on the top sp2 carbon, the adjacent sp3 carbon bearing H and $C{H}_3$, $H_{3}C$ on the left ring carbon) + a bicyclo[3.2.0]heptadiene bearing a gem-dimethyl ($H_{3}C$, $C{H}_3$) and a further $C{H}_3$ [?]; the first product –hν (downward arrow)→ another trimethylcycloheptatriene (sp3 carbon bearing $H_{3}C$ and H, $C{H}_3$ on the adjacent sp2 carbon, $H_{3}C$ on the left ring carbon) [?] (drawing poorly reproduced; exact positions of the methyl groups uncertain); (ii) a 4a-methyl-octahydronaphthalene (angular $C{H}_3$) with a ring C=C next to the ring junction, bearing on a ring carbon an OH and a 1-hydroxyethyl group (HO, HO, $H_{3}C$) –(i) $p\mathrm{\text{–}}C{H}_3{C}_6{H}_{4}S{O}_{2}Cl$, pyridine (ii) $CaC{O}_3$ [?]→ ring-expanded bicyclic ketone: a cycloheptenone fused to a cyclohexane, with angular $C{H}_3$ at the ring junction, the ring C=O and a $H_{3}C$ on the carbon alpha to the C=O, and a C=C next to the ring junction [?] (drawing poorly reproduced)] [2004/45m/8a]

56. Provide mechanism for the following reactions:

[Figure: (i) bicyclo[3.2.0]hept-2-ene (cyclopentene fused to cyclobutane) bearing on the cyclobutane carbon C-7 an OAc and an H, and on C-6 a D and an H (stereochemistry as drawn: OAc and D on wedge-type bonds, H on the other bonds) –Δ, 300°C→ bicyclo[2.2.1]hept-2-ene (norbornene) bearing OAc on one carbon of the saturated two-carbon bridge (with H) and D on the adjacent carbon (with H), the stereochemistry being shown (1,3-sigmatropic shift); (ii) 2-methoxytropone (cyclohepta-2,4,6-trien-1-one with $C{H}_{3}O$ on C-2) –hν→ ? –hν→ 7-methoxybicyclo[3.2.0]hept-6-en-2-one (cyclopentanone fused to a cyclobutene; C=O on the five-membered ring adjacent to a ring-junction carbon; $OC{H}_3$ on the cyclobutene double-bond carbon next to that junction)] [2003/20m/1b]

57. Write the structure of the product(s) in the following reactions with mechanism:

[Figure: (i) $C{H}_3-CO-C{H}_2-C{H}_2-CH{\left(C{H}_3\right)}_2$ –hν→ ; (ii) butanal ($C{H}_{3}C{H}_{2}C{H}_{2}CHO$) + 2-methylbut-2-ene (${\left(C{H}_3\right)}_{2}C=CH-C{H}_3$) –hν→ ; (iii) a bicyclic cyclopropyl ketone: carbocyclic ring fused to a cyclopropane, drawn in perspective, with a benzoyl group $C(=O)-C_6{H}_5$ on a cyclopropane ring-fusion carbon [?] –hν→ ; (iv) 2 × trans-2-butene ($C{H}_3-CH=CH-C{H}_3$, methyls trans) –hν→] [2003/20m/5c]

58. Compound A is photochromic (it becomes coloured on exposure to light). The process is reversible giving back the starting material in the dark. Propose a structure for the coloured photoisomer B.

[Figure: A ⇌ B (forward arrow labelled hν, reverse arrow labelled “dark”). A = a xanthone-derived tricyclic: benzene ring fused to a pyran-4-one (C=O at the top, ring O at the bottom), which is fused to a third six-membered ring carrying, going round from the carbonyl side: C(Ph)(OH), C(CN)2, C(CN)= and =C(Ph) next to the ring-O side (i.e. a ring C=C bearing CN and Ph)] [2002/20m/1b(ii)]

59. Provide mechanism for the following transformations:

[Figure: 2,2-dimethylcyclohexanone –hν→ B = 6-methylhept-5-enal (OHC–CH2–CH2–CH2–CH=C(Me)Me). A = cis,cis-cycloocta-1,3-diene –hν→ B = bicyclo[4.2.0]oct-7-ene (cyclobutene fused to cyclohexane); A –hν, Sensitizer→ C = (E,Z)-cycloocta-1,3-diene (one trans double bond) –Δ→ B] [2002/30m/6b(ii)]

60. Give mechanism of the following transformations:

[Figure: (i) A = 3-phenylbutan-2-one (Ph and Me on the chiral carbon, Me on wedge) –Per acid→ B = 1-phenylethyl acetate, Ph(Me)CH–O–C(=O)–Me, configuration retained (87%) + C = methyl 2-phenylpropanoate, Ph(Me)CH–C(=O)–O–Me (13%). (ii) A = CH3–CO–C(=CH2)–CH2–CHR2 (an α-methylene ketone with a CHR2 group at the γ-position) [?] –hν→ B = cyclobutanol: C1 bearing OH and CH3, C2 bearing =CH2, the carbon across bearing R, R [?] + C = cyclobutane bearing CH3–C(=O)– on one carbon and R, R on the opposite carbon [?]. (iii) A = cyclobutanecarbonyl azide (C4H7–C(=O)N3) –hν, H2O→ B = cyclobutylamine. (iv) A = ten-membered ring (cyclodecane) bearing at one carbon HO and CH3 and at a transannular carbon HO and O [?] –H2O/H3O+→ B = ten-membered ring bearing O and CH3 at one carbon and C=O at the transannular carbon [?] (drawing poorly legible)] [2002/15m/7c]

61. Draw structures of all the products which are expected to be formed in the following reactions:

[Figure: (i) cyclohex-2-en-1-one + ${\left(C{H}_3\right)}_{2}C=C{H}_2$ (isobutylene) –hν→ ?; (ii) $C_6{H}_{5}CHO$ + $C{H}_{3}CH=CHC{H}_3$ (2-butene drawn with the two CH3 on the same side, cis) –hν→ ?] [2001/20m/6b]

62. Predict the products in the following reactions and suggest their mechanisms.

[Figure: (i) 2-ethylbenzophenone (benzene ring with CH2CH3 and, ortho to it, C(=O)Ph) –(hν, 2-propanol)→ (product not shown) (ii) R–C(=O)–(CH2)2–CH2–R′ –(hν)→ (product not shown) (iii) α,β-unsaturated ketone drawn skeletally: C=O carbon bearing a short vertical stub (CH3) and attached to CH=C, the β-carbon carrying R and a second R (printed “ᶦR”, possibly R′ [?]) –(hν)→ (product not shown)] [2000/20m/5d]

63. Predict the major products in the photochemical reactions and propose mechanisms.

[Figure: (i) C6H5–C(=O)–CH2–CH2–CH3 (butyrophenone) –(hν)→ (ii) bicyclic β-lactone drawn as two fused squares: in the right-hand four-membered ring the top-right corner carbon carries =O and the bottom-right corner is a ring O (2-oxabicyclo[2.2.0]hexan-3-one skeleton; no double bond visible in the left ring) –(hν over arrow; 77 K under arrow)→] [2000/15m/6d]

64. Predict the major product of the photochemical reaction and give their mechanisms. (i) Methyl butyrate (ii)

[Figure: Cyclic ketone drawn as a seven-membered ring [?]: C=O at the top; going round, the ring carbon left of the carbonyl’s neighbour bears two Ph groups and the corresponding carbon on the right bears two Ph groups, with a two-carbon bottom edge (3,3,6,6-tetraphenylcycloheptanone as drawn [?]); no reagent or arrow printed] [2000/15m/7d]

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Last updated: 30 October 2026