ir&nmr problems

Problem 1 C5H10O MW 86

The band at 1716 indicates a carbonyl, probably a ketone. The bands at 3000-2850 indicate C-H alkane stretches.

Problem 1, NMR intrepreted

Problem2C7H14O

MW 114The band at 1718 indicates a carbonyl, probably a ketone. The bands at 3000-2850 indicate C-H alkane stretches.

Prob 2 NMR, interpreted

Problem 3 C4H10OMW 74

The broad band at 3339 indicates O-H stretch, probably an alcohol. The bands at 3000-2850 indicate C-H alkane stretches. The band at 1041 is C-O stretch, consistent with an alcohol.


Problem 4 C6H14O

MW 102The broad band at 3350 indicates O-H stretch, probably an alcohol. The bands at 3000-2850 indicate C-H alkane stretches. The bands from 1320-1000 indicate C-O

stretch, consistent with an alcohol.


Note that the structure has a chiral center and the mixture is racemic. Methylene protons adjacent to a chiral center may not be identical.

Problem 5 C4H8O2

MW 88Prob 5, IR answer

The band at 1743 indicates a carbonyl, probably a saturated aliphatic ester. The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1320-1000 could be due to C-O stretch, consistent with an ester.


Problem 6 C5H10O2


The band at 1740 indicates a carbonyl, probably a saturated aliphatic ester. The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1320-1000 could be due to C-O stretch, consistent with an ester.



Prob 7, IR answerThe band at 1728 indicates a carbonyl, probably an aldehyde; an aldehyde is also suggested by the band at 2719 which is likely the C-H stretch of the H-C=O group.

The bands at 3000-2850 indicate C-H alkane stretches.


Problem 8 C8H8O


The band at 1703 indicates a carbonyl; that the carbonyl is an aldehyde is suggested by the bands at 2828 and 2733 (C-H stretch of the H-C=O group). The bands at 3000-2850 indicate C-H alkane stretches. The band (unmarked on the graph below) just to the left of 3000 indicates aromatic C-H stretch. Aromatics also show

bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane).


Note: There are 4 aromatic protons (B, 7-8 ppm), indicating a disubstituted aromatic ring. You are not expected to assign the individual peaks in the aromatic region to specific hydrogens on the aromatic ring. The aromatic protons show a pattern characteristic of para substitution.

Problem 9 C9H10O2


The band at 1697 indicates an alpha, beta-unsaturated carbonyl; that the carbonyl is an aldehyde is suggested by the bands at 2828 and 2739 (C-H stretch of the H-C=O group). The bands at 3000-2850 indicate C-H alkane stretches. The band (unmarked on the graph below) just to the left of 3000 indicates aromatic C-H stretch.

Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane).


Problem 10 C3H6O2


The band at 1716 indicates a carbonyl. The wide band from 3300-2500 is characteristic of the O-H stretch of carboxylic acids. The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1320-1000 indicate the C-O stretch of carboxylic acids.


Problem 11 C11H14O2


The band at 1684 indicates a carbonyl. The wide band from 3300-2500 is characteristic of the O-H stretch of carboxylic acids. The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1320-1000 indicate the C-O stretch of carboxylic acids. The band (unmarked on the graph below) just to the left of 3000

indicates aromatic C-H stretch. Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane).


Problem 12 C8H8O2


The band at 1684 indicates a carbonyl. The wide band from 3300-2500 is characteristic of the O-H stretch of carboxylic acids. The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1320-1000 indicate the C-O stretch of carboxylic acids. The band just to the left of 3000 (3065) indicates aromatic C-H

stretch. Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane).


Problem 13 C7H9N


The two bands at 3433 and 3354 indicate a secondary amine. The bands at 3000-2850 indicate C-H alkane stretches. The band at 3034 indicates aromatic C-H stretch; aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane). C-N stretch of aromatic amines

would show up at 1335-1250 (there is a band in that region).


Problem 14 C5H13NMW 87

Prob 14, IR answerThe two bands at 3388 and 3292 indicate a secondary amine. The bands at 3000-2850 indicate C-H alkane stretches.


Problem 15 C8H14O


The band at 1718 indicates a carbonyl, probably a ketone. The bands at 3000-2850 indicate C-H alkane stretches. Since the compound is an alkene, one would expect to see C=C stretch at 1680-1640; these weak bands are not seen in this IR (according to Silverstein, "the C=C stretching mode of unconjugated alkenes usually shows

moderate to weka absorption at 1667-1640"). Since the compound is an alkene, C-H stretch should appear above 3000 (not seen: the absorption for this single hydrogen must be too weak).

Problem 16 C4H9Br


The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1300-1150 could indicate C-H wag (-CH2Br) of an alkyl halide.



Prob 17, IR answerThe bands at 3000-2850 indicate C-H alkane stretches; the small (unmarked) band just to the left of 3000 indicates aromatic C-H stretch. Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane). The wide band in the region 3500-3200 indicates the O-H stretch of

an alcohol or phenol.


Problem 18 C13H10O3


The band at 1682 indicates a carbonyl, probably an ester. The band at 3192 indicates C-H aromatic stretch; aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane). The wide band just to the left of the 3192 band indicates O-H stretch (alcohols and phenols).


Note: the correct placement of the -OH on the ring and the arrangement of the ester may be beyond the scope of your spectroscopy course. See this explanation.

http://orgchem.colorado.edu/hndbksupport/spectprob/18/18struct.html

Problem 18, structure

Problem 19 C8H14


The bands at 3000-2850 indicate C-H alkane stretches. There really aren't many other bands in the spectrum to indicate functional groups. The compound is an alkyne; we would expect to see a carbon-carbon triple bond stretch at 2260-2100, however, this is a weak band at best and often does not show up on IR.


Note: The integral values for A, B, and C need to be multiplied by 2 to get a total of 14 protons in the molecule. By convention, integral values on an nmr are reported as the lowest common multiple.

Problem 20 C9H13N


The bands at 3000-2850 indicate C-H alkane stretches. The band at 3028 indicates C-H aromatic stretch; aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane). The bands in the region 1250-1020 could be due to C-N stretch. The weak, broad banc at about

3500 could be amine N-H stretch or it could be a slight contamination of an impurity (water) in the sample.


Problem 21 C9H10


The bands at 3000-2850 indicate C-H alkane stretches. The band at 3060 indicates C-H aromatic stretch; aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane).

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