Abid Khan 2897438 | WEEK 3 & 5 FRIDAY 8AM

Determining the Identity of an Organic Compound through Functional Group Testing and

Spectral Analysis

Abid Khan 1

Abstract

The aim of this investigation was to determine the structure of a given unknown organic compound by

conducting functional group tests and deducing its identity through IR and NMR spectroscopy.

Functional group tests were conducted to identify a preliminary understanding of the functional groups

present. Infrared and Nuclear Magnetic Resonance Spectroscopy were used to further identify the

functional groups present and the compound’s carbon-hydrogen framework. Three potential

compounds, namely 2-pentanone, 3-pentanone and 1-pentanal, were listed as the possible unknown

compound. After observing the qualitative observations during the functional group tests and spectral

analysis, it was determined that the unknown compound was 2-pentanone.

Introduction/Aim

The study of organic-containing compounds and their properties is called organic chemistry. Organic

chemistry plays a vital role for understanding living systems. The synthetic fibres, plastics, artificial

sweeteners, and drugs that are an accepted part of modern life are products of organic chemistry

(Zumdahl, 2005). An important part of organic compounds are functional groups. A functional group

is a specific group of atoms within a molecules that is responsible for the characteristic chemical

reactions of that molecule (Marie, 2014). They are attached to the carbon backbone of organic molecules

and are far less stable than the carbon backbone so they are likely to participate in chemical reactions

(Fromm, 1997). Functional groups are important as a specific set of functional groups in any given

organic compound specifies its role and chemical behaviour (Dallas Learning Solutions, 2014).

Determining the structure of atoms and molecules of organic compounds can come from studying their

interaction with light (Michigan State University, 2000). Different regions of the electromagnetic

spectrum provide different kind of information as a result of such interactions. The three types of

spectroscopy that will be utilised in this investigation are infrared spectroscopy (IR), nuclear magnetic

resonance spectroscopy (NMR) and mass spectroscopy. The infrared region of the electromagnetic

spectrum covers the range from just above the visible range (7.8 × 10-7m) to 10-4m (McMurry, 2011).

Absorption of this lower energy radiation causes vibrational and rotational excitation of groups of atoms

within the molecule (Michigan State University, 2000). Since different functional groups have different

characteristic absorptions, identification of functional groups through IR spectroscopy is easily

accomplished (Michigan State University, 2000). NMR spectroscopy is the most valuable spectroscopic

technique available for laboratory organic chemists for structure determination (McMurry, 2011).

Absorption in the low energy radio frequency part of the electromagnetic spectrum causes excitation of

nuclear spin states and are tuned to certain nuclei (1H, 13C, 19F and 31P) (Michigan State University,

2000). For a given type of nucleus, NMR spectroscopy distinguishes and counts atoms in different

locations in the molecule (Michigan State University, 2000).

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The aim of this investigation is to determine the structure of a given unknown organic compound by

conducting functional group tests and deducing its identity through IR and NMR spectroscopy.

Methods

For the methods of this investigation, please refer to pages 10-23 of the 2014MSC Organic Chemistry

Laboratory Manual 2014 edition.

Results

The results section contains tables and descriptions presenting the recorded qualitative observations for

the functional groups and elements testing and physical constants (boiling point and refractive index),

solubility and oxygen flask test results for the unknown compound. These data can be analysed to form

a preliminary understanding of the identity and structure of the unknown compound. A brief description

of each of the functional group tests along with its chemical equation or reaction mechanism are

illustrated. The findings from the IR, NMR and mass spectroscopy for the unknown compound are

presented to assist in deducing the identity of the organic compound. The IR, NMR and mass

spectroscopy spectra can be found in the Appendix. Three potential compounds are then listed with

their physical constants along with their respective chemical structures.

Qualitative Observations

Table 1.1, presented on page 3, presents the qualitative observations that were observed while

conducting the standard functional group and element tests that were conducted by oxygen flask

method. The colour and opacity of the resulting solution, along with whether a precipitate (ppt) was

present, were noted for each of the tests.

Table 1.2, presented on page 4, presents the qualitative observations for the unknown organic

compound. The results detail the observations and whether the unknown compounds are positive or

negative to the standard functional group tests which can then be used to identify the functional groups

present.

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Table 1.1 – Qualitative observations from the Standard Functional Group/Element Tests

Table 1.1 - Qualitative Observations from Standard Functional Group/Element Testing

Station Number/Reaction Name

Reactant being

changed

Functional

Group/Element Test Observation

1.a - Reaction with bromine

Cyclohexane

Carbon-carbon

double bond

Red colour change, no ppt

Cyclohexene

Red colour decolourised,

transparent

1.b Reaction with permanganate

Cyclohexane

Strong violet colour, no

ppt

Cyclohexene dark red, no ppt

2.a - Solubility of alcohol and

phenol in base

Benzyl Alcohol

Hydroxyl group

Clear, transparent

Phenol

slightly yellow colour

change, not dissolved

100%

2.b - Reaction of phenol with ferric

chloride Phenol clear

2.c - Reaction with phenol and

aqueous bromine Phenol

White cloudy colour

change, ppt formed

2.d - Luca's Test for tertiary

aliphatic alcohol

Tert-butyl

alcohol

2 phases, cloudy in the

bottom, clear on top

3.a - Reaction of carboxylic acid

with sodium bicarbonate Benzoic acid Carboxylic acid group

Not soluble, crystal ppt

formed

3.b (i) - D.N.P Test Acetophenone Ketone group

Opaque orange-red colour,

ppt formed

3.b (ii) - Iodoform Test Acetophenone Methyl ketone

Milky colour change, ppt

formed

3.c (i) - Tollen's test Benzaldehyde

Aldehyde group

Silver mirror, dark green,

ppt formed

3.c (ii) - Reduction of Fehling's

solution Glucose

Dark red, opaque, ppt

formed

3.c (iii) - Reaction of aldehyde with

permanganate Benzaldehyde Opaque, dark violet, no ppt

3.c (iv) - D.N.P Test Benzaldehyde Opaque orange ppt

3.d - Hydroxamic Test Methyl Benzoate Ester group Opaque purple/black color

4.a - Solubility of amines in

aqueous acid

Aniline

Amino Group

Slightly yellow, soluble

Acetanilide White ppt, not soluble

4.b - Test for primary aromatic

amine Aniline

Dark red, ppt formed,

silver top

4.c - Reaction of aromatic amines

and aqueous bromine Aniline

Cream-coloured ppt, not

soluble

5. - Test for nitro compounds m-dinitrobenzene Nitro group

Yellow ppt, cloudy,

cream-coloured liquid

6.a - Distinguishing between ethers

and hydrocarbons Diethyl ether Ether group Brown colour change

6.b (i) - Testing for sulphur ions - Sulphur ion White ppt

6.b (ii) - Testing for organic halide

ions -

Chlorine, bromine,

iodine ion White ppt

6.b (iii) - Testing for nitrogen ion - Nitrogen ion Green colour change

7. - Smokey flame test for

Aromatics Ethyl acetate Aromatic group Melted, smokey flame

8. - Molisch's Test for sugars Glucose Carbohydrate Dark purple colour

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Table 1.2 – Qualitative Observations from the Functional Group/Element Testing for the

Unknown Organic Compound

Table 1.2 - Qualitative Observations from Functional Group/ Element Testing For Unknown Compound

Station Number/Reaction Name

Functional

Group/Element Test Observation

Positive/Negative with

Standard Functional Group

test

1.a - Reaction with bromine

Carbon-carbon

double bond

Red colour, no ppt,

soluble

positive with cyclohexane

standard

1.b Reaction with permanganate

Strong violet

colour, no ppt

positive with cyclohexane

standard

2.a - Solubility of alcohol and

phenol in base

Hydroxyl group

Clear

positive with benzyl alcohol

standard

2.b - Reaction of phenol with ferric

chloride

Slightly yellow

colour change negative

2.c - Reaction with phenol and

aqueous bromine Red colour change negative

2.d - Luca's Test for tertiary

aliphatic alcohol Clear, transparent negative

3.a - Reaction of carboxylic acid

with sodium bicarbonate

Carboxylic Acid

group

Soluble, no sound

heard negative

3.b(i) - D.N.P Test Ketone group

Orange colour, ppt

formed positive

3.b(ii) - Iodoform Test Methyl Ketone

Opaque, cloudy, no

ppt negative

3.c (i) - Tollen's test

Aldehyde group

Clear, transparent,

no ppt negative

3.c (ii) - Reduction of Fehling's

solution

N.R, no colour

change from blue negative

3.c (iii) - Reaction of aldehyde with

permanganate

Opaque, dark

violet positive

3.c (iv) - D.N.P Test Opaque orange ppt positive

3.d - Hydroxamic Test Ester group

Clear on top, ppt

present positive

4.a - Solubility of amines in aqueous

acid

Amino group

Clear transparent,

no ppt negative

4.b - Test for primary aromatic

amine

Light brown, white

top, not clear negative

4.c - Reaction of aromatic amines

and aqueous bromine

Dark yellow colour

change negative

5. - Test for nitro Compounds Nitro group Purple, no ppt negative

6.a - Distinguishing between ethers

and hydrocarbons Ether group

Brown colour

change positive

6.b (i) - Testing for sulphur ion Sulphur ion Clear, NR negative

6.b (ii) - Testing for organic halide

ion

Chlorine, bromine,

iodine ions Clear, no ppt negative

6.b (iii) - Testing for nitrogen ion Nitrogen ion

Clear, no colour

change negative

7. - Smokey flame test for aromatics Aromatic group No smokey flame negative

8. - Molisch's Test for sugars Carbohydrate Dark red, no ppt negative

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Description and Illustration of the Standard Functional Group Tests

1.a – Reaction of Cyclohexane and Cyclohexene with bromine

In this reaction, bromine acts as an electrophile and is very ‘polarisable’ by the approaching pi bond

from the alkene. One of the bromine atoms becomes attached to both carbon atoms, with a positive

charge being found on the bromine atom. The bromonium ion then gets attacked in the back by a

bromide ion. This allows the decolourisation of the bromine (red to transparent). This is an example of

electrophilic addition of alkenes (Clark, 2000). Alkanes do not have a pi bond and are sp3 hybridised

thus they cannot make an induced dipole on bromine.

1.b – Reaction of Cyclohexane and Cyclohexene with permanganate

When an organic compound reacts with dilute alkaline potassium manganate (VII) solution in the cold

to give a green solution followed by a dark brown precipitate, then the compound may contain a carbon-

carbon double bond. The chemical equations where the reactants are cyclohexane and cyclohexene are

illustrated below.

When cyclohexene reacts with the purple potassium manganate (VII), manganese dioxide is formed

and induces a brown colour change.

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The IR spectrum for cyclohexane

and cyclohexene are very similar

and differ only by the characteristic

absorption of a carbon double bond

C=C at 1640-1680 cm-1.

2.a – Distinguishing between alcohol and phenol by solubility in base and comparison of IR spectrum

between toluene and benzyl alcohol

Phenols are about a million times more acidic than alcohol and are therefore soluble in dilute sodium

hydroxide. Phenols are more acidic because the phenoxide ion is resonance-stabilised. Delocalisation

of the negative charge over the ortho and para positions of the aromatic ring results in increased stability

of the phenoxide anion relative to undissociated phenol (McMurry, 2011). Therefore this test can be

used to distinguish between alcohol and phenol.

Benzyl alcohol has a broad absorption at 3400 - 3650 cm-1 while toluene does not. Toluene can be

resonance stabilised. The resonance hybrid suggests all six C=C bonds of benzene are more than the

single bonds but not complete double bonds as they only have partial pi character.

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2.b – Reaction of phenols with ferric chloride in pyridine

Treatment of phenol with anhydrous ferric chloride and pyridine produces a blue, violet, purple, green

or red-brown solution.

2.c – Reaction with phenol and aqueous bromine

The –OH group attached to the benzene ring in phenol has the effect of increasing its reactivity (Clark,

2000). The net effect of this is that the –OH group has a 2,4 – directing effect meaning that the incoming

groups of bromide will tend to go into the 2-position or 4-position. This causes decolourisation of

bromine and a white precipitate is formed.

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2.d – Luca’s Test for tertiary aliphatic alcohols

The reaction mechanism for the Luca’s test is a substitution nucleophilic unimolecular reaction (SN1)

with a tertiary alcohol. This results in two distinct phases that should immediately separate.

3.a – Reaction of carboxylic acid with sodium bicarbonate and comparison of IR spectrum of benzoic

acid and toluene

Carboxylic acids are soluble in aqueous sodium bicarbonate. In this reaction, the crystal of benzoic acid

is dissolved and forms colourless sodium ethanoate.

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Benzoic acid has characteristic absorptions for carbonyl group 1670 – 1780 cm-1, hydroxyl group at

2500 - 3100 cm-1 and C-O bond at 1210 – 1320 cm-1 which toluene does not have. These characteristics

are the stretching frequencies for carboxylic acid.

3.b (i) – D.N.P Test with acetophenone

The D.N.P test with acetophenone is used to determine whether a ketone group is present. The following

reaction mechanism outlines this reaction

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3.b (ii) – Iodoform Test – test for methyl ketones and IR spectrum of acetophenone

The following reaction is used to determine whether a methyl ketone is present. Iodine is decolourised

indicating that one of the reactants were a methyl ketone.

Acetophenone has a carbonyl group that is part of the functional group. The stretching frequency of this

group is 1670 – 1780 cm-1.

3.c (i) – Tollen’s test for aldehyde

The Tollen’s test refers to the oxidation of aldehyde. In this reaction, a silver mirror is formed and a

silver colouration can be seen around the solution indicating that an aldehyde is present.

3.c (ii) – Reduction of Fehlings’ Solution

Fehlings’ solution contains copper (II) ions complexed

with tartrate ions in sodium hydroxide solution. In this

reaction an aldehyde/sugar is reduced to a reducing

sugar and forming a red precipitate of copper (I) oxide.

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3.c (iii) – Reaction with permanganate

Aldehydes can react with permanganate and induces the colour change from orange to green. The

resulting product is benzoic acid.

3.c (iv) – IR spectrum of benzaldehyde

Benzaldehyde has a characteristic C=O stretch of 1690 – 1720 cm-1 which toluene does not have.

3.e – Stretching frequencies of carbonyl and N-H group in amides

The N-H stretching frequency in aniline is 3300 – 3500 cm-1 while the carbonyl group in acetanilide has

a stretching frequency of 1690 – 1720 cm-1.

4.a – Solubility of amines in aqueous acid

Aniline is soluble in acid as it is a basic amine. There is a lone pair of electrons on the nitrogen and the

tendency of the nitrogen to share its lone pair of electrons with acids is responsible for the basic

character of amines. The positive charge can then be delocalised giving a resonance structure.

Acetanilide is an amide and due to its structure cannot delocalise and thus is not soluble in acid.

Amine Amide

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4.b – Test for primary aromatic amine.

Step 1 – Reaction between aniline, sodium nitrite (converted to nitrous acid in situ) and hydrochloric

acid.

When aromatic amines are coupled with diazonium cations, diazonium coupling competes with a

nucleophilic attack of the amine's nitrogen on the diazonium cation's terminal nitrogen, as the strength

of the resulting N-N single bond does not considerably differ from that of the C-N single bond

(Chemgapedia, 2013). This reaction occurs at low temperatures only

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Step 2 – β-napthol in sodium hydroxide mixed with diazonium cation

This reaction occurs in low temperatures only and an intense orange-red precipitate is formed.

Physical Properties of the Unknown Compound

The unknown compound is a clear, colourless and transparent liquid. The boiling point of the compound

is 102oC and has a refractive index of 1.3905.

Peaks in IR and NMR spectra of the Unknown Compound

After analysing the IR and NMR spectra of the unknown compound which can be found in the appendix,

the following peaks were found.

Table 1.3 - Observations after the analysis of IR spectra of the unknown compound

Table 1.3 - Observations after the analysis of IR spectra of the unknown compound

Ketone/Ester/Carboxylic Acid/Aldehyde group 1680 – 1780 cm-1 (sharp)

Alkyl group 2853 – 2962 cm-1 (medium/sharp)

Isopropyl group 1385 – 1395 cm-1 (medium)

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Table 1.4 - Observations after the analysis of 1H NMR spectra of the unknown compound

4 signals/peaks are observed in the 1H NMR spectra of the unknown compound.

Table 1.4 - Observations after the analysis of 1H NMR spectra of the unknown compound

Triplet @ 0.93 ppm 3 H

Sextet @ 1.60 ppm 2 H

Singlet @ 2.13 ppm 3 H

Triplet @ 2.40 ppm 2 H

Table 1.5 - Observations after the analysis of 13C NMR spectra of the unknown compound

Observations after the analysis of 13C NMR spectra of the unknown compound

Peak @ 13.7 ppm Primary Alkyl

Peak @ 17.41 ppm Primary Alkyl/Secondary Alkyl/Tertiary Alkyl

Peak @ 29.78 ppm Primary Alkyl/Secondary Alkyl/ Tertiary Alkyl

Peak @ 45.71 ppm Primary Alkyl/Secondary Alkyl/ Tertiary

Alkyl/Ether

Peak @ 208.93 Aldehyde/Ketone

Potential Compounds

After observing both the IR and NMR spectra, it can be deduced that the compound is either an

aldehyde or a ketone as both these functional groups are present in the IR and 13C NMR spectra.

Three possible compounds that are clear liquids and have a boiling point near 102oC are: 2-pentanone,

3-pentanone, 1-pentanal. These compounds were suggested by the convenor of 2014MSC Organic

Chemistry.

Name: 2-pentanone

B.P: 101oC - 102oC

Name: 3-pentanone

B.P: 100oC - 102oC

Name: 1-pentanal

B.P: 102oC - 103oC

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Discussion

The identity of the given unknown organic compound can be deduced by analysing: the qualitative

observations and whether the functional group tests were positive or negative, the NMR spectra to

determine the number of carbon atoms and different proton environments and the IR spectra to further

deduce what functional groups were present. The structures of 2-pentaanone, 3-pentanone and 1-

pentanal will be examined using the results that have been obtained.

In table 1.2 the unknown compound had positive reactions with following functional group tests:

carbon-carbon double bond group, hydroxyl group, ketone group, aldehyde group, ester group and ether

group. This finding indicates that the unknown compound could contain one or more of these functional

groups.

The IR spectra results can be used to further narrow down the actual composition of the functional

groups. As seen from the IR spectra located in the appendix and tabulated in table 1.3, there is a sharp

peak at the absorption frequency of 1680 – 1780 cm-1. This indicates that there functional group present

could be a ketone, ester, carboxylic acid or an aldehyde. Furthermore, there is a medium/sharp peak at

the absorption frequency of 2853 – 2962 cm-1 suggesting that there are alkyl groups in the unknown

compound. Lastly, there is medium peak at the absorption frequency of 1385 – 1395 cm-1 indicating

that there are isopropyl groups present in the compound. After analysing the IR spectra findings, the

following potential groups that were hypothesised from the findings in table 1.2 can be rejected:

hydroxyl group, ether group and carbon-carbon double bond group.

To determine the actual structure and carbon backbone of the unknown compound, the NMR spectra

results in table 1.4 and table 1.5 will be analysed. As shown in table 1.5 and the 13C NMR spectra in the

appendix, there are five peaks indicating that there are five different carbon environments in the

unknown compound. This seems to suggest that 3-pentanone is not the unknown compound as it does

not contain 5 different carbon environments. This is highlighted in figure 1.1. The different carbon

environments are shown by the coloured circles.

Figure 1.1 – Carbon environments in 3-pentanone

As it can be seen in figure 1.1, there are only 3 different

carbon atoms thus 3-pentanone cannot be the unknown

organic compound.

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1

2

3

4

5

To distinguish between 2-propanone and 1-pentanal, as both compounds have five different carbon

environments, the 1H NMR spectra results will be analysed to identify their different proton

environments. Both compounds have 4 different proton environments. In table 1.4 and from the 1H

NMR spectra in the appendix, it can be observed that there is singlet at 2.13ppm. This suggests that the

proton group at 2.13ppm has no neighbouring protons. This finding appears to eliminate 1-pentanal as

the unknown compound as each proton environment has at least one neighbouring proton. This is

illustrated in figure 1.2 by using the program Chemdraw.

Figure 1.2 – Neighbouring proton environments in 1-pentanal

Therefore it can be concluded that 2-pentaanone is the unknown organic compound tested in this

investigation. This can be further justified by labelling the 1H NMR spectra results with their respective

peaks.

Figure 1.3 – The splitting pattern of 2-pentanone

1. –CH3 group, singlet (3H)

2. –C=O group

3. –CH2 group, triplet (2H)

4. –CH2 group, sextet (2H)

5. –CH3 group, triplet (3H)

When observing the results from table 1.2, positive reactions were noted for the hydroxyl group, carbon-

carbon double bond and ether groups. These results may have arisen from experimental errors. It was

noted during the investigation that the amount of compound was depleted during these functional group

tests and thus the required amount of the compound were not inserted. This may have caused the

incorrect observations. For next time, more efficient use of the amount of the compound must be

conducted in order to insert the correct amount of the compound in each functional group test.

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Conclusion

The aim of this investigation was to determine the structure of a given unknown organic compound by

conducting functional group tests and deducing its identity through IR and NMR spectroscopy. After

observing the qualitative observations during the functional group tests and spectral analysis, it was

determined that the unknown compound was 2-pentanone.

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Appendix

IR Spectrum of Unknown Organic Compound

1H NMR spectra of unknown organic compound

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13C NMR spectra of unknown organic compound

Mass spectra of unknown organic compound

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References

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l.html

[Accessed 1 May 2014].

Clark, J., 2000. Ring Reactions of Phenol. [Online]

Available at: http://www.chemguide.co.uk/organicprops/phenol/ring.html

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Dallas Learning Solutions, 2014. Biomolecules. [Online]

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[Accessed 29 April 2014].

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Available at: http://www.3rd1000.com/chem301/chem301a.htm

[Accessed 21 April 2014].

Marie, A., 2014. Functional Groups Definition. [Online]

Available at: http://chemistry.about.com/od/chemistryglossary/a/fungroupsdef.htm

[Accessed 20 April 2014].

McMurry, J., 2011. Organic Chemistry with Biological Applications. 2nd ed. California: Cengage

Learning.

Michigan State University, 2000. Introduction to Spectroscopy. [Online]

Available at: http://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/spectrpy/spectro.htm

[Accessed 29 April 2014].

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