Question

1. Explain how each spectroscopy (IR, Mass spec, and NMR) method works- what are you observing? What is happening to the molecule that gives rise to useful information.

2. Explain how to read each: IR, NMR, mass spec.

3. Why are -OH and -NH signals in both proton NMR and the IR region relatively broad in appearance? Explain how the appearance of the -OH stretch would change in the IR spectrum of an alcohol was take in the gas phase and not the liquid phase.

4. A. Why do protons and carbons next to electronegative atoms have their resonances shifted downfield? B. An aromatic ring or double bond proton (or carbon) has a resonance shifted very far downfield. Explain why this is so with a sketch.

5. Using CH3CHBr2 Sketch the predicted NMR spectrum. Include integration and splitting.

Answer 1

1. NMR spectroscopy, mass spectrometry, and IR spectroscopy all these techniques used to identifying the structure and composition of an unknown sample

Spectroscopy:- Light passing through a sample and looking at what frequencies of light are transmitted

Infrared (IR) spectroscopy:- uses infrared radiation to analyze a sample.

Nuclear magnetic resonance (NMR):- takes advantage of the spin states of protons to identify a compound

mass spectrometry:-ionization of a sample by bombarding it with high-energy electrons

2. NMR:-

Note and count the number of peaks. Remember to ignore solvent peaks.

It is common for you to be able to assign only some of the peaks. Others might have to be grouped
if they are too similar.

Collect other data and constraints. find out the Molecular weight and Functional groups present.
IR:- We can observe the“singing” of bonds using IR radiation to a sample and measuring the frequencies at which the radiation is absorbed. in this technique identifying the bonds present in a given molecule.

mass spec. :- it is just a relative amount of each mass fragment. Putting them together into likely molecules is done with a little math.

4. A.Protons and carbons next to electronegative atoms have their resonances shifted downfield because of electron density and electronegativity. If higher electronegativity difference then more shifted.

B. High electron density of neighbouring atoms may shield the nucleus from an external
magnetic field. If there is little or no electron density in nearby atoms or groups, the
nucleus can also be deshielded.

5.