14C_s11_lec01_e02_key

Chemistry 14c lecture 1 spring 2011 exam 2 solutions

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Unformatted text preview: contain at least one oxygen atom. Chemistry 14C Lecture 1 Spring 2011 Exam 2 Solutions Page 3 Oxygens Nitrogens 68 - O - N = H Formula Comments 1 0 68 - 16 - 0 = 52 C14H52O Rejected; violates H-rule 2 0 68 - 32 - 0 = 36 C14H36O2 Rejected; violates H-rule 3 0 68 - 48 - 0 = 20 C14H20O3 Reasonable 4 0 68 - 64 - 0 = 4 C14H4O4 Rejected; more than four signals in 1H-NMR 1 2 68 - 16 - 28 = 24 C14H24N2O Rejected; poor fit for 1H-NMR integration 2 2 68 - 32 - 28 = 8 C14H8N2O2 Rejected; poor fit for 1H-NMR integration Formula (C15): 236 - 180 (C14) = 56 amu for oxygen, nitrogen, and hydrogen. The 1749 cm-1 peak in the IR spectrum is due to a C=O stretch, so the formula must contain at least one oxygen atom. Oxygens Nitrogens 56 - O - N = H Formula Comments 1 0 56 - 16 - 0 = 40 C15H40O Rejected; violates H-rule 2 0 56 - 32 - 0 = 24 C15H24O2 Rejected; poor fit for 1H-NMR integration 3 0 56 - 48 - 0 = 8 C15H8O3 Rejected; poor fit for 1H-NMR integration 1 2 56 - 16 - 28 = 12 C15H12N2O Rejected; poor fit for 1H-NMR integration DBE: 14 - (20/2) + (0/2) + 1 = 5 Five rings and/or pi bonds. Benzene ring possible. IR: Zone 1: Alcohol O–H: Present - strong, broad peak ~3450 cm-1. Amine/amide N–H: Absent - no peak in zone 1. Terminal alkyne ≡C–H: Absent - no peak in zone 1. Zone 2: Aryl/vinyl sp2 C–H: Present - peaks above 3000 cm-1. Alkyl sp3 C–H: Present - peaks below 3000 cm-1. Aldehyde C–H: Absent - no peak ~2700 cm-1. Carboxylic acid O–H: Absent - zone 2 peaks not broad enough. Zone 3: Alkyne C≡C: Absent - no peak ~ 2200 cm-1; not enough DBE for C=O plus C≡C plus benzene ring. Nitrile C≡N: Absent - no peak ~ 2200 cm-1; not enough DBE for C=O plus C≡N plus benzene ring. Zone 4: C=O: Present @ 1749 cm-1. Could be ester or ketone; 13C-NMR confirms ester. Zone 5: Benzene ring: Present - peaks at ~1600 cm-1 and ~ 1500 cm-1. Alkene C=C: Absent - peak at ~1600 cm-1 but not enough DBE for C=C plus C=O plus benzene ring. Chemistry 14C Lecture 1 1 Spring 2011 Exam 2 Solutions Page 4 H-NMR: Chemical shift Splitting Integral #H Implications 7.42–7...
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This note was uploaded on 09/06/2011 for the course CHEM 140A taught by Professor Whiteshell during the Fall '04 term at UCSD.

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