AS and a Level Chemistry a Multiple Choice Practice Tests (Alcohols, Haloalkanes and Analysis)

Infrared Questions NIS Analytical Chemistry Worksheet #2 Name:______

A B C D

butan-1-ol, butan- butanoic acid, Butane, and butan-2-one butanal, butan-2- 2-one, butanal. one, butane

1 a). In the table above discuss how infrared Spectroscopy could be used to differentiate the compounds in EACH group from one another?

1 b). Which group of compounds could not be differentiated from each other using infrared spectroscopy? Why

2. Which type of bond is NOT linked to high levels of IR absorption and the greenhouse effect? Explain

A B C D

C–H C=O C–O O–H

3. Which statement(s) is/are true about the compound pentan-3-one?

1) Why will, this compound show IR absorbance at 3200 cm-1 2) Why will it have a characteristic IR absorbance around 1700 cm–1.

4. This question is going to give you 3 isomeric compounds and three IR spectra. What you have to do is to match each compound to its correct spectrum. You will find a list of useful infrared absorption data after the three spectra. The absorption data for bonds is included. The three compounds you are concerned with are propanoic acid: CH3CH2COOH methyl ethanoate: CH3COOCH3 hydroxypropanone: CH3COCH2OH a) Draw full structural formulae for the three compounds so that you can see exactly which bonds you need to think about. b) Decide which compound corresponds to each of the spectra below, explaining how you made your decisions.

ANSWERS

1.A All of these are diagnostic region. Butanol has an O-H peak which is broad and long above 3200cm-1 (an alcohol (not an acid), 1700 for the butan-2-one as it is a ketone. So could be differentiated from one another as they are quite different and separated.

B All of these are diagnostic region. This is a Carboxylic acid so would have a broad and deep peak 3000 and lower, and the butanal could be distinguished from it as it is much lower at 1700 cm-1

C All of these are diagnostic region. Butane C-H bond near 3000 and C=O near 1700

D Butanone and butanal BOTH have C=O bond and would overlap and be indistinguishable Thus 1B) D is the answer

2.A C–H, Methane has 4 of these bonds and has a high greenhouse potential.

B C=O Carbon dioxide has 2 of these bonds and has a high greenhouse potential.

C C–O Correct answer. This bond type is not found amongst the most potent greenhouse gases.

D O–H Water has two of these bonds and has a high greenhouse potential. 4. Spectrum 1: Notice the small troughs close to 3000 cm-1 which are due to C-H bonds. The spectrum shows the presence of the C=O bond by the trough at about 1750 cm-1,But there certainly isn't an O-H bond present either in an alcohol or an acid. The only structure

without an O-H bond is the ester, methyl ethanoate.

Spectrum 2: This is showing an absorption due to an O-H bond but in an alcohol (not a CA) as it is high around 3400 cm-1 (acids are lower as @ 3000) So, the absorbance is and not an acid. At 1700 cm-1, we are showing a C=O bond. So there is an O-H group and a separate C=O group. The molecule is hydroxypropanone. (the is an alcohol and ketone)

Spectrum 3: The key absorption here is very wide trough either side of 3000 cm-1 characteristic of a carboxylic acid. So this has to be propanoic acid. But you might also notice the absorption at about 1700 cm-1 due to the C=O bond in the acid.