Question

1. Describe the process of taking an IRS Spectrum both on mechanically level and on a molecular level, what is being analyzed and why it happens. (You may answer in paragraph or flow chart format.)

2. Draw a mechanism for the dehydration of 4-methyl cyclohexanol using sulfuric acid

3.Explain why volatile solvents are often used to prepare mass spectroscopy samples and why in the GC/MS analysis the first few minutes are not analyzed.

4. Give a brief summary as to how IR and other types of spectruscopy helped advanced the feild of chemistry. (Please Cite)

Answer 1

1.Infrared spectroscopy involves the interaction of IR radiation with matter. It is used to identify and study chemicals be it a solid,liquid or gas.

An IR instrument consist of an IR light source, a sample holder, a means of selecting individual wavelength of light, a device for plotting the amount of light absorbed as function of wavelength or frequency. The plot is referred to as IR spectrum.

The IR spectrum of sample is recorded by passing beam of infrared light through the sample. When the frequency of IR is the same as vibrational frequency of a bond Absorption occurs. Examination of transmitted light reveals how much energy was absorbed at each frequency( wavelength). The entire wavelength range is measured using Fourier Transform instrument and then absorbance spectrum is generated.

An unknown sample whose structure is not known can be analyzed using IR spectrum. Functional groups present in molecule can be found.

2.

3. Sample preparation using volatile solvent for mass spectrometry:

Proper sample preparation is crucial for obtaining good results with mass spectra. Volatile solvent are used in most cases because they will pass the mass spectrometer and they dont leave residue behind which will hinder the accurate result.

The first few minutes are not analyzed in GC instrument because it vaporizes the sample and then separates and analyzes various components. The time elapsed between injection and elution is called Retention time.

4. Mentioned are a few of spectroscopic methods that led to the advancement of field of chemistry. They are:

a) Structural elucidation of organic compounds by IR spectra and NMR spectra,molecular weight determination by mass spectra.

b) It is used in detecting molecules, macromolecules such as protein, DNA, polysaccharides and chemical bonds.

c) UV- Visible molecular spectrometry is used in quantitative determination of transition metal ions, highly conjugated organic compounds and biological macromolecules.

d) Raman spectroscopy: used in chemical structure elucidation and in polymer analysis.