chem lab activity 6

nuclear magnetic resonance spectroscopy (NMR)

measures the magnetic field around all the hydrogen atoms in a molecule to give proximity to a functional group & proximity to other hydrogens, important for structure determination

infrared spectroscopy (IR)

studies the different frequencies of infrared light that a molecule absorbs to indicate the functional groups present

3500 cycle/cm

O-H bonds present

1710 cycles/cm

C=O in ketones & aldehydes present

used less often

NMR & IR

Lucas test

based on the fact that lower molecular weight alcohols are soluble in the solution, which helps the alcohol react with the reagent to form alkyl chlorides which are no longer soluble in the mixture. This creates a cloudiness and turbidity as more of the alkyl chloride is formed

what is Lucas reagent made of?

zinc chloride & hydrochloric acid

immediate reaction w/ Lucas reagent

tertiary alcohol

reaction within 5 minutes of mixing with Lucas reagent

secondary alcohol

no reaction with Lucas reagent

primary alcohol

Lucas test reaction

Lucas test on

1-pentanol, 2-pentanol, 2-methyl-2-butanol, and 3-pentanone

iodoform test

If a methyl ketone is present it will react with iodine in a basic solution in order to form an iodoform which is a yellow crystalline solid.

iodoform reaction

iodoform test on

2-pentanone and 3-pentanone

Tollen’s test

using reagent in the presence of an aldehyde there will be a formation of a silver mirror in the reaction vessel. This is caused by an oxidation of the aldehyde to a carboxylic acid and the silver ions are reduced to metallic silver which creates the silver mirror.

what is Tollen’s test unique to

aldehydes

what is Tollen’s reagent made of?

silver nitrate & ammonia

Tollen’s reaction

Tollens test on

benzaldehyde

2,4-DNPH test

When an aldehyde or ketone is treated with 2,4-DNPH, a crystalline precipitate with a unique color will form.

2,4-DNPH reaction

2,4-DNPH test on

3-pentanol and 3-pentanone

hydroxamate test

results in the formation of a colored complex when an ester is heated with hydroxylamine, followed by the addition of ferric (Fe3+) ions

hydroxamate reaction

hydroxomate test on

Aspirin and Salicylic Acid