CHE 344 Due Thue, Jan. 18, 2018 t. Infrared spectroscopy is most useful for iden

Question

CHE 344 Due Thue, Jan. 18, 2018 t. Infrared spectroscopy is most useful for identifying Take Hom 9. Ethene has a UV absorption at Amas 171 nm. Do you functional groups. What organic functional group porresponds to each of the following sets of IR absorptions? expect 1,3-butadiene to have an absorption maximum at a longer or shorter wavelength than that of ethene? Explain using the molecular orbital diagram shown here a) 1650 om (strong) and one spike around 3300-3400 cm and 2825 cm (moderate) and 1715 om (strong) b) 1710 cm (strong), 2720 cm (weak) Antibonding molecular orbitals ) 2500-3500 cm t (very broad) «, . LUMO excitatiorn excitation 2 Both cyclohexene and 1-hexyne have the molecular formula Cattho. How coukd you use IR spectroscopy to distinguish between these two compounds (i.e. what absorptions would you look for in the IR spectrum that are characteristic of each compound?). You can use HOMO | Bonding molecular orbitals (HOMO) back side of this page 4 Which of the following is True (T) or False (F) when an organic molecule absorbs ultraviolet radiation: Ethene 1,3-butadiene a) Electrons are excited from the HOMO to the LUMO b) Electrons are excited from the LUMO to the c) Amas increases with extended conjugation in d) Amax decreases with extended conjugation in HOMO the molecule the molecule transitions 10. Plants are green due to the presence of the "organic" compound chlorophyll (an organometallic, shown at right) Which of the following must be true (T) or false (F) about chlorophyll? e) e is larger for + . than for n . a) chlorophyll has extended 5. Which of the following molecules will have its ultraviolet conjugation Amas absorption at the longest wavelength? Explairn --b) chlorophyll absorbs green light. c) chlorophyll absorbs red wavelengths in the visible region and reflects green. d) you could measure chlorophyll concentrations using Beer's law The most energetically favorable electron transition in the UV spectrum of 1,3-butadiene is 6. 11. A mass spectrometer sorts ions on the basis of their to c)n+ 12. In the following MS Which two (2) of the following compounds can have both an r-n° and .. * electron transitions in their UV region? 7. spectrum: 80 a) Which is the molecular ion (M.,)" 20 b) Which is the base peak? 10 20 30 4 60 8. You would expect lycopene (shown below) to be m/z 13. A prominent MS (M.-18) a) Coloriess due to the lack of carbonyls b) Coloriess due to absence of phenyl rings. o) Completely transparent since it is an alkene d) Highly colored due to extended conjugation. d) Highly colored due to being aromatic. peak suggests that the compound might be a) a ketone c) an alcohol d) a 1° amine e) an ester b) an aldehyde

Explanation / Answer

1) IR spectrum absorption :

Amide shows C=O stretch (strong ) absorption at 1650-1690cm-1 and N-H stretch band at 3200-3400cm-1

(-CO-NH- )

2) Aldehyde (-CH=O) shows C=O stretch at 1700-1720 cm-1(strong absorption ) and aldehydic C-H stretch in the frequency range 2700-2850 cm-1

3)carboxylic acid group (-COOH) shows -C=O stretch (strong) in the frequency range 1700-1720 cm-1 and a very broad band for -OH stretch in the frequency range 2500-3500 cm-1

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

---