BIOCHEM LAB - Experiment 1: Qualitative Tests for Identification of Functional Groups in Organic Compounds

Functional Group

• Structural features that make it possible to classify compounds into families.

• Group of atoms in an organic compound that has a characteristic chemical behavior.

• Behaves in nearly the same way in every molecule it is part of.

Unsaturated

Given to compounds containing carbon-carbon double bond or triple bond, like alkenes and alkynes

Alkanes

Only contain carbon-carbon single bonds

Benzene

Contains alternating carbon-carbon double bonds in its ring system, but it is not considered unsaturated due to the differences in its properties in comparison to alkene

Aromatic

Other term for benzene, because it was originally derived from aromatic substances

Von Baeyer’s Test for Unsaturation

Ability of potassium permanganate (KMnO4) to oxidize the carbon-carbon double bonds of alkenes to glycol and carbon-carbon triple bond of alkynes to carboxylic acids

KMnO4

Formula of potassium permanganate

Purple/Violet

Color of Potassium Permanganate

Brown

Color of the precipitate of Manganese dioxide

MnO4

Formula of Manganese dioxide

Positive test for unsaturation (Von Baeyer’s test)

The disappearance of the characteristic violet color of KMnO4 and appearance of a brown precipitate

Bromine Test for Unsaturation

It adds to the carbon-carbon double bond of alkenes to produce dibromoalkanes and reacts with alkynes to produce tetrabromoalkanes.

Dark red-orange

Color of Bromine

Positive test for unsaturation (Bromine Test)

The nearly instantaneous disappearance of the dark red-orange color.

Alcohols

have the hydroxyl (-OH) functional group attached to a saturated carbon with the general formula R-OH.

Phenol

-OH is attached to a benzene ring

Boardwell-Wellman Test

Uses potassium dichromate dissolved in sulfuric acid.

Orange-yellow solution

Color of potassium dichromate

K2Cr2O7

Formula of potassium dichromate

Presence of hexavalent chromium (Cr^6+)

Why does potassium dichromate have an orange-yellow color?

Hexavalent Chromium (Cr^6+)

Oxidizes primary and secondary alcohols into carboxylic acid and ketone.

Greenish color

Color of chromic ion

Indicator for the presence of a primary or secondary alcohol

Color change from yellow to green (Boardwell-Wellman Test)

Brown

Color of phenol

Due to the production of benzoquinone

Why does phenol have a brown color?

C6H4O2

Formula of benzoquinone

Lucas Test

Used to distinguish primary, secondary, and tertiary alcohols. The reagent is a mixture of concentrated hydrochloric acid and zinc chloride, which converts alcohols to the corresponding alkyl chlorides

Primary Alcohols

No appreciable reaction

Secondary Alcohols

React more rapidly (Slow)

Tertiary Alcohol

React very rapidly (fast)

Positive test for Lucas Test

Formation of a second layer or and emulsion

Ferric Chloride Test

A very specific test for the detection of phenols

OH- group of phenols

forms a complex with ferric ion (Fe³+)

Orange

Color of ferric chloride

Violet

Color of ferric ion

Positive test for ferric chloride test

Color change from orange to violet

Aldehydes and Ketones

Share the carbonyl functional group which features carbon doubly bonded to oxygen (C=O)

Aldehydes

At least one hydrogen bonded to the carbonyl group; the other attachment may be to a carbon or a hydrogen

Ketones

Two carbon atoms bonded to the carbonyl carbon and no hydrogen

2,4 - Dinitrophenylhydrazine (2,4-DNP)

Commonly used for qualitative detection of carbonyl groups of aldehydes and ketones

Positive result of 2,4-dinitrophenylhydrazine

formation of (2,4-DNP), which is seen as yellow or orange-red precipitate

Tollen’s Test

A common method for distinguishing between aldehydes and ketones is based mainly on the fact that aldehydes can be oxidized in normal conditions, while ketones cannot.

Positive test of Tollen’s Test

Indicates the presence of aldehydes, whereas no reaction occurs with ketones

Tollen’s Reagent

• Consists of silver ammonia complex in an ammonia solution.

• This reagent oxidizes aldehydes to the corresponding carboxylic acids; silver ion is reduced to elemental silver

Ag(NH3)2+

Formula of silver ammonia complex

Elemental Silver

Deposited as a silver mirror on the wall of clean test tube.

Positive test for Tollen’s Test

The formation of the silver mirror on precipitate.

Yellow or orange-red precipitate

Color of precipitation of (2,4-DNP)

Carboxylic Acid

Also contain a carbonyl group, at least one hydroxyl (-OH) group attached to the carbonyl group in a common carbon.

Carbonyl Group

• (-COOH)

• it behaves as a weak acid, known for their irritating odors

Sodium Bicarbonate Test

Acids undergo neutralization reactions with bases, such as hydroxides, carbonates, and bicarbonates. The product is usually salt and water

Carboxylic acid reacts with sodium bicarbonate solution

Producing carbon dioxide as evidence by a brisk effervescence with concomitant of carboxylate salt

NaHCO3

Formula of Sodium bicarbonate

Positive test for sodium bicarbonate test

Brisk effervescence