Question

2. (2 pts.) Provided below are IR spectra of 1,2,3,6-tetrahydrobenzaldehyde (I) and 3-methyl-2-cyclohexen-1-one (II). Decide which of the IR spectra A and B corresponds to which structure (I or II). On each spectrum, identify the peaks that are associated with a specific bond vibration bond by drawing the functional group for that bond, circling the specific vibrating bond and drawing an arrow from the circled bond to the absorption peak, as appropriate. Include all the C-H bonds. odo and II 1,2,3,6-tetrahydrobenzaldehyde 3-methyl-2-cyclohexen-1-one 100 A Anh 1661 1193 890 3027 2710 1438 668 2841 2922 1726 1000 9000 Bood

Answer 1

Answer: IR Spectrum A corresponds to aldehyde compound 2922 cm 1720 cm 1661 cm C=C 1661 cm 1 C=0 1720 cm =C-H 3012 cm -C-H 2922 cm 1 C-H in aldehyde 2710 and 2841 cm" (Н 2710 cm 2841 cm 3012 cm 1 There is no resonance possible between double bond and carbonyl compound C=O appear in higher frequency region IR Spectrum B corresponds to aldehyde compound 1687 cm C=C 1632 cm 3031 cm CEO 1687 cm =C-H 3031 cm Η 1632 cm 1 -C-H 2941 cm 2941 cm The carbonly carbon is in resonance with double bond hence the stretching is low for C=C and C=0 than in the aldehyde compound (no resonance) Hence the Spectra A is the aldehyde compound The spectra B is the unsaturated ketone compound.