Can you answer all question?These questions are containing IR spectroscopy problems and I need to...

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Can you answer all question?These questions are containing IR spectroscopy problems and I need to help me to resolve these problems.
	
Document Preview: Chemical Analysis Activity Sheet 3 - IR spectroscopy Question 1 a) An oxygen-containing compound shows an absorption band at ?l700 cm-1 and no absorption bands at ?3300 cm-1, ?2700 cm-1, or ?ll00 cm-1. What class of compound is it?b) A nitrogen-containing compound shows no absorption band at 3400 cm-1 and no absorption hands between 1700 cm-1 and 1600 cm-1. What class of compound is it?Question 2 How could IR spectroscopy distinguish between the following?a) a ketone and an aldehyde d. cis-2-hexene and trans-2-hexeneb) a cyclic ketone and an open-chain ketone c) benzene and cyclohexene d) a primary amine and a tertiary amineQuestion 3 A compound with molecular formula C4H6O has the IR spectrum below. Identify the compound.Question 4	For each of the IR spectra below, four possible compounds are shown. In each case, indicate which of the four compounds is responsible for the spectrum.Question 5 For each of the following IR spectra indicate which of the five given compounds is responsible for the spectrum.Question 6 Each of the IR spectra shown below is the spectrum of one of the following compounds. Identify the compound that is responsible for each spectrum.Question 7 The IR spectrum shown below is the spectrum of one of the following compounds. Identify the compound.Question 8:What molecular events lead to absorption of radiation in IR spectroscopy?What would the IR spectrum of the N2 and O2 molecules look like? Explain.How do you prepare samples (solids/liquids/gases) for measurement of their IR spectra?How is the absorption of IR radiation related to the ‘greenhouse’ and ‘enhanced greenhouse’ effect?

Robert · Accepted Answer

IR and Combined
Chemical Analysis Activity Sheet 3 - IR spectroscopy  
 
Question 1  
a) An oxygen-containing compound shows an absorption band at l700 cm-1 and 
no absorption bands at 3300 cm-1, 2700 cm-1, or ll00 cm-1. What class of 
compound is it? 
Answer:  The compound might be a carbonyl compound.  Around 1700 cm-1 
carbonyl stretching happens. No absorption at other positions eliminates 
alcohol, ester and ether etc.  
 
b) A nitrogen-containing compound shows no absorption band at 3400 cm-1 and 
no absorption hands between 1700 cm-1 and 1600 cm-1. What class of 
compound is it? 
Answer:  Absence of band at 3400 means there is no N-H stretching. No band 
between 1700 and 1600 suggests that there are no carbonyl groups. So amides 
can be eliminated. As the compound contain N and there is no N-H stretching 
at 3400 cm-1, the compound might me, a tertiary amine. 
 
Question 2  
How could IR spectroscopy distinguish between the following? 
 
a) a ketone and an aldehyde 
Answer:  Both Ketone and aldehyde shows an absorption at around 1700 cm-1. But 
aldehydes contain a C-H bond and that C-H stretching happens at around 2700- 
2800cm-1. Ketone do not have C-H bond stretching. The presence and absence of 
things band will help to distinguish between aldehyde and ketone. 
  
d. cis-2-hexene and trans-2-hexene 
Answer: C=C stretching usually happens between 1670 and 1640 cm-1. Cis isomer is 
less symmetric. So a cis isomer absorbs always stronger than a trans isomer. 
 
c) a cyclic ketone and an open-chain ketone 
Answer: Open chain ketones have sp2 hybridisation at the carbonal carbon and 
the bond angle is 120 degrees. It absorbs at the normal absorption  range of 
around 1700 cm-1. 
In the case of cyclic ketones, there is a possibility of ring strain at the carbonyl 
carbon and because of this, the bond angle varies.  This will cause a change in 
absorption. If the ring size becomes smaller, absorption happens at an 
enhanced  frequency. When the ring expands, it happens at a shorter 
frequency.
d) benzene and cyclohexene  
Answer: Aromatic C-H stretching happens at 3070 cm-1. So in benzene only absorption 
will be at 3070 cm-1.  Also there is aromatic C=C bending between 1700 to 1500 cm-1 
In the case of cyclohexene,

Can you answer all question? These questions are containing IR spectroscopy problems and I need to help me to resolve these problems. Document Preview: Chemical Analysis Activity Sheet 3 - IR...

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