All Chemical Identification Stuff for Organic Chemistry 2

Colorado Mesa Univserity - Richards OChem 2 Class

O-H in IR

3200-3600(strong and broad)

N-H

3200-3600(medium and broad, one for each NH)

O-H (RCO2H)

2500-3600 (strong and very broad)

C-H(sp)

3200-3300(strong)

C-H(sp2)

3000-3200(variable, depends on number of groups)

C-H(sp3)

2850-3000(variable, depends on number of groups)

O=C-H

2750 and 2850(two sharp peaks, may be masked)

C=-N

2220-2260(medium)

C=-C

2100-2260(medium, narrow)

C=C

1600-1700(medium, narrow)

C=C(Ar)

1500 and 1600(two narrow peaks)

C=O

1600-1800(very strong)

C-O

1050-1250(strong)

C-N

1020-1230(medium to strong)

Spectroscopy

study of the interaction of matter and electromagnetic radiaion(light)

Frecuency(v)

number of waves per unit time (number of waves per second, Hz)

Wavelengths

distance between wave crests

Wavenumber

number of waves per unit distance(# of waves per cm,cm^-1)

Which type of vibrations are we most interested in in IR Spectroscopy?

Stretching vibrations

How does IR spectroscopy work?

A light source is shined at a sample, some of the light is absorbed by the sample and some light is TRANSMITTED through the sample to the detector. The light that is transmitted is what we’re seeing.

What can the amount of light be quantified as?

absorbance or percent transmittance

Where do you spend most of your time in an IR Spectrum?

above 1400 (anything lower is the fingerprint region, above is the functional group region)

The higher the peak in IR…

the higher the absorbance

What can you use IR Spectroscopy for?

determine functional groups present

What determines the wavenumber of absorbance?

atomic mass, bond strength

What determines bond strength?

type of bond (C=-C, C=C, C-C), hybridization, and resonance

What factors determine intensity of absorbtion?

Polarity (more polar more intense absorbance) and number of bonds (more bonds, more intense absorbance)

What determines the broadness of absorbance?

H-bonding

What is H-Bonding?

When an electronegative atom (O,N,F) steals the H’s from other atoms.

Why is the O-H bond so broad?

Because of hydrogen bonding which allows interactions with neighboring atoms. The oxygen hydrogen bond stretching vibrations vary in frequencies vs one sharp frequency.

The lighter the atoms…

the higher the wavenumber

The stronger the bond in IR…

the higher the wavenumber because stronger bonds require more energy to vibrate.

Methyl

15

Ethyl

29

Propyl

43

Butyl

57

Pentyl

71

Chlorine

35

Bromine

79

With each addition of a carbon chain how much do you add to the previous MS number? (Ex: ethyl 29 + ? = propyl)

14

What does the y-axis represent in a MS graph?

Abundance of fragments

What does the x-axis represent on a MS graph?

Molecular Weight(MW)

What is the molecular ion peak?

The highest molecular weight fragment that is the most significant(tells the molecular weight for the original compound)

What is the base peak?

Tallest peak (can be important, just depends)

What determines fragmentation abundance?

Stability and similar MW despite a different fragment piece.

What does an odd molecular ion peak mean?

Presence of Nitrogen

What does it mean if the M+2 peak has one that’s 1/3 the size of the M peak?

Potentially the presence of chlorine

What if the M+2 peak is the same size of the M peak?

Potential presence of Bromine

Phenyl

77

Formyl

29

Acetyl

43

Which fragment will be shown in the MS graph?

Positive ones

What happens when the beam hits an electron?

The electron gets knocked out of orbit and turns the atom positively charge.

What is the first step after injecting your sample in Mass Spectroscopy?

A neutral sample molecule gets shot with an electron beam and an electron will get ejected and turn the molecule positively charged.

What happens after a molecule is positively charged in Mass Spectroscopy.

Molecular Ion (radical cation) gets fragmented into smaller pieces and the positive fragments gets read in the instrument.

Ionization Energy

E it takes to lose an electron

Which electron will be removed?

Highest energy electron

What are the two types of fragmentation for Alkyl Chloride/Bromide and Ethers?

Heterolytic Fragmentation and alpha cleavage(homolytic fragmentation)

What is heterolytic fragmentation?

fragmentation of the X or O bond. (results in a peak we CAN see)

Draw the mechanism for a heterolytic fragmentation for CH3-CH(Cl)-CH3 and CH3CH2CH(CH3)-O-CH(CH3)-CH3.

INSERT PHOTO(2)

Draw the mechanism for an alpha cleavage for CH3-CH(Cl)-CH3 and CH3CH2CH(CH3)-O-CH(CH3)-CH3.

INSERT PHOTO(2)

What two types of fragmentation do Alcohols do?

Dehydration (heterolytic fragmentation) and alpha cleavage.

Draw a mechanism for dehydration of CH3CH2CH(H)CH2-CH(OH)-CH3

INSERT PHOTO

How much mass do you lose and which hydrogen is used for dehydration?

lose 18 and the 3rd hydrogen

Why are some fragments more abundent?

Increased stability, different fragments but same MW

2* amide

165-175

ester

165-175

carboxylic acid

175-185

aldehyde

190-200

ketone

205-220

C=N

150-170

Ar-C

110-170

TMS(Reference)

0

Primary Alkyl -CH3

0.7-1.3

Secondary Alkyl -Ch2- in H NMR

1.2-1.6

Tertiary Alkyl

1.4-1.8

Allylic

1.6-2.2

Methyl Ketone

2.0-2.4

Aromatic Methyl

2.4-2.7

Alkyne

2.5-3.0

Alkyl Halide

2.5-4.0

Alcohol

2.5-5.0

Alcohol, Ether

3.3-4.5

Vinylic

4.5-6.5

Aryl

6.5-8.0

Aldehyde

9.7-10.0

Carboxylic Acid

11.0-12.0

What does Nuclear Magnetic Resonance do?

It uses radio waves to interact w/ matter, its used to look at a nuclei that have a non-zero value for their quantum spin number.

What does Nuclear Magnetic Resonance show us?

Tells us about the carbon and hydrogen framework.

What is the spin state of a nucleus affected by?

An applied magnetic field

What happens when you remove a charge?

You create a magnetic fireld

What’s the orientation of a nucleus’s magnetic field without any applied magnetic field?

random

What are the two types of spin states?

Alpha(same direction) and Beta(anti-parallel)

What are the steps for Nuclear Magnetic Resonance?

Proton gets shot w/ MF and absorbs or releases radio waves .

What does the energy difference between the spin states depend on?

The strength of the magnetic field felt by the nuclei

What does the strength felt by the MF on the nuclei depend on?

Strength of the applied MF and the amount of shielding around the nucleus

What does a more electron rich environment mean?

More shielding

Nuclei in different electron environment absorb light at…

different energys (frequencies)

Upfield

goes to right

Downfield

goes to the left