Final Orgo Lab

Spectroscopy

Spectroscopy

Is the branch of science that studies the interaction between light and matter. It is mainly used for structure determination

Principle of Spectroscopy

Measuring the response of molecules after absorbing a certain amount of energy.

Electromagnetic Radiation

Electromagnetic Radiation has wave-like & particle-Like properties

Infrared Spectroscopy “IR”

The functional groups present or absent

Ultraviolet-Visible Spectrometry “UV-VIS”

Conjugated Systems

Identification of Functional Groups by IR (How does it work???)

• Stretching of bonds is a change of state “length”. \n • Each change of state requires a specific amount of energy. \n • This amount of energy is equal to the difference in energy between the two states “energy gap” \n • Each bond has its own specific energy gap. \n • We irradiate the molecule with light having all frequencies (energy) and then we determine which one \n “frequency” is missing. \n • The missing frequency was absorbed by the molecule.

Jones Oxidation

Oxidizes primary & secondary alcohols and aldehydes (turns Blue Green)

Lucas Test

It is used to differentiate between primary, secondary & tertiary alcohols

The reagents used are HCl with ZnCl2

Primary- NR

Secondary-turbid solution in a couple of minutes

Tertiary-turbid solution quickly

Ferric Chloride Test

• It is used to test for phenols.

• Phenol forms red-blue-violet complex with Fe(III)

Derivative Test

• Convert aldehydes and ketones into other derivatives.

• 2,4-dinitrophenylhydrazine & semicarbazone

• They convert liquid aldehydes and ketones into solids.

Tollen’s Test

• It is used to test for aldehydes

• The reagents used are AgNO3 and HO-

• The aldehyde is oxidized to carboxylic acid.

• Ag(I) is reduced to Ag (silver mirror)

Iodoform Test

• Test for presence of methyl ketones

• Reagents used are iodine (I2) and (HO-)

• It gives a carboxylate and Iodoform (ICl3) (yellow precipitate)

Bromine Test

• Test for presence of double or triple bonds

• Reagents used are iodine (Br2) (red color)

• Bromine adds to the double bond or triple bonds and since it is consumed the red color disappears

Permanganate Test

• Test for presence of double or triple bonds

• Reagents used are KMnO4 & HO- (purple color)

• It adds two hydroxyl groups to the double bond

• Since the permanganate is consumed the color disappears

Atomic size

As atomic size decreases, the bond length decreases and the wavenumber increases.

AS bond length decreases,

wavenumber INCREASES

Bond Strength

As bond strength increases, the wavenumber increases

Effect of Hybridization

Effect of Resonance

Resonance decreases the wavenumber

Intensity

As bond polarity increases, the signal intensity increases

Effect of Hydrogen Bonding “Alcohols”

•Concentrated alcohols (too many H-Bonds) will have a broad signal

• Diluted alcohols give narrower signals

IR Single Bonds

appear below 1500 cm-1

IR Double bonds

appear between 1600-1850 cm-1

IR Triple Bonds

appear between 2100-2300 cm-1

X-H (O-H, N-H, C-H)bonds

appear between 2700-4000 cm-1

Carboxylic acid IR

Alkene

• note the peaks between 1600-1850

• to conform a C=C-H bond, there should be a small peak at 3100

Alkyne

• note peaks around 2100-2300

• C(triple)C-H will have peak at 3300

Alcohol

• Board band around 3200-3600

Primary Amine

• two short peaks after 3000

Secondary Amine

• one peak after 3000

Conjugation ==

lower wavenumber 1750 to 1680

IR tips

Hint: Tetrasubstituted alkenes and internal alkynes have no signals in the designated regions.

As conjugation increases

gap decreases, λmax increases

Woodward Fieser rules: base line

217 nm

Woodward Fieser rules: each extra double bond

add 30 for each

Woodward Fieser rules: auxochromic alkyl group

add 5 for each

Woodward Fieser rules: each exocyclic double bond

add 5 for each

one carbon of the double is in a defined ring and the other carbon of the double bond is not

Woodward Fieser rules: homoannular diene

add 39

Which of the following is the least soluble in water?

A. Alcohols

B. Secondary Amines

C. Primary Amines

D. Carboxylic acids

B. Secondary Amines

Dehydration of cyclohexanol follows:

A. Markovnikov’s Rule

B. Zaitsev’s Rule

C. Evelyn Effect

D. Hallalov Rule

B. Zaitsev’s Rule

In the dehydration mechanism, the first step is:

A. Formation of the carbocation

B. Protonation of the “OH” group

C. Loss of a proton

D. Rearrangement

Protonation of the “OH” group

Dehydration reaction is done in a distillation apparatus:

A. The alkene is toxic

B. To push the equilibrium to the right

C. To push the equilibrium to the left

D. To condense the reactants back

B. To push the equilibrium to the right

Draw the product of the dehydration reaction of

SN1 reactions

-Unimolecular

-polar protic solvents

-carbocation

-tertiary and secondary halides

-AgNO3 in ethanol

-SN1 depends on ALKYL HALIDE

SN2 reactions

-Bimolecular

- polar aprotic solvents

-primary and secondary halides

-NaI in acetone

-SN2 depends on BOTH ALKYL HALIDE AND NUCLEOPHILE

Zaitzev’s rule

an elimination reaction the major product is the more stable alkene with the more highly substituted double bond

Markovnikov’s rule

When HZ is added to unsymmetrical alkene, the hydrogen will add to the carbon with the most number of hydrogens

E1 mechanism

E2 mechanism

Evelyn effect

the product composition changes during the course of the reaction

Its hypothesized that the reason is because of the starting mixture of cis- and trans- isomers

What equipment is used in fractional distillation?

Vigreux column

Mass Spectrometry

It is used to detect the molecular weight and molecular formula

Ionization

Bombard molecule with a high energy electron beam to eject an electron and form a radical cation

Radical Cation

Also called, molecular ion or the parent ion and it has a mass equal to that of the original \n compound. Radical cations are unstable and rapidly fragment into smaller ions and radicals.

base peak

highest peak

molecular ion

its weight is equal to the molecular weight of the compound

base peak does not always equal

the molecular ion peak

Nitrogen Rule

• Odd Molecular weight = Odd number of nitrogen \n atoms \n • Even Molecular weight = No nitrogen or even number \n of nitrogen atoms.

Bromine in mass spec

Will have a 1:1 ratio

Chlorine in mass spec

Will have a 3:1 ratio

Analysis (M+1)+. Peak

Intensity (M+1) = (# of carbons x (% abundance) x Intensity [M]) / 100

In our reduction experiment, hydrogen has two roles

making the catalyst and reducing the trans cinnamic acid

A Grignard reagent is

• a carbon nucleophile

• made from alkyl halide and Mg

• cannot react with water if we want a successful Grignard reaction

Methyl benzoate