Question

Two infrared spectra are shown with the molecular formula CH10. One is the spectrum of cyclohexene, and the other is the spectrum of 2-hexyne. Identify each and explain your reasons for making the identification. Spectrum A Spectrum B 08 DA 06 DS TRANSMITTANCE Re Trance 02 DSCH 4000 1900 NESTO Waverunteront NEST Christy Bottom goriche Which of the following compounds gives an infrared spectrum with peaks at 3300 cm (strong, broad peak) and 1640 cm-- (sharp, weak peak)? OH OH o e a Two infrared spectra of molecules are below. One is the spectrum of cyclopentane, and the other is the spectrum of cyclopentene. Identify each and explain your reasons for making the identification. Spectrum A Spectrum B 08 06 TRANSMITTANCE Heative Transmittance 04 02 3000 2000 L000 wavenumber comm NIST Chemistry Webbock http://webstock.i.gov/chemistry 0.96 3000 2000 1000 Wavenumber(cm-11 NIST Chemistry Webbook retp://webbock is gonemokryl

Answer 1

ANSWER:

Question 1 - Cyclohexene and 2-hexyne

• Cyclohexene spectrum will show two characteristically signals: the C=C stretch at approx 1650 cm-1 and C-H stretch for sp2 carbons at 3100-3000 cm-1.
• The stretch for the triple bond C-C of an alkynee appears at 2200-2100 cm-1, however, as 2-hexyne is an internal alkyne it is probably that this stretch won't be observed in the IR spectrum. So, the main signals in the IR spectra of 2-hexyne will be the C-H stretch for sp3 carbons (3000-2800 cm-1)
• Then, spectrum A correspond to cyclohexene and the compound of spectrum B is 2-hexyne

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Question 2 -

• A strong a broad band at 3300 cm-1 is typically for the O-H stretch of an alcohol group
• At the same time the band at 1640 cm-1 correspond to C=C stretch for an alkene.
• Then, the third structure is the only that will show this two peaks.
  • ​​​​​​​First compound is an ether and the main peak is the C-O stretch at 1200 cm-1
  • Second compound is ketone and the main peak is the C=O stretch at 1720 cm-1
  • Four compound is alcohol and the main peak is the O-H stretch at 3300 cm-1

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Question 3 - Cyclopentane and cyclopentene

• Cyclopentane spectrum will show a strong band for C-H stretch for sp3 carbons (3000-2800 cm-1) and C-H bend
• Cyclopentene spectrum will show two characteristically signals: the C=C stretch at approx 1650 cm-1 (weak and small band becuase this is a symmetric alkene) and C-H stretch for sp2 carbons at 3100-3000 cm-1.
• Then, spectrum A correspond to cyclopentane and the compound of spectrum B is cyclopentene

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