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Spectroscopy Questions

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1) Give the Frequency ranges (in cm-1) for each of the following:
a. O-H stretch
b. aldehyde
c. -C-H stretch
d. =C-H stretch
2) Briefly describe how could you distinguish between cyclohexane and cyclohexene by IR?
3) Define the following terms:
a. Coupling constant
b. Chemical shift
c. Spin-spin coupling.
4) A solid samples are prepared by examination by IR spectroscopy by fusing them in a KBr pellet or dissolving them in CCl4 and subtracting a background of pure CCl4 from the spectrum. Assuming equal solubility of the compound in both solvents why would acetone be a poor substitute for CCl4 in the latter method.
5) Predict the splitting pattern for each kind of proton in the 1H NMR spectra of the following:
a. CH3CH2CH2Br
b.
6) Predict the number of signals that would appear in the 13C NMR spectra of the molecules from the previous questions.
7) Propose a structure for a molecule with a molecular formula C10H13NO and the following 1H NMR data. Explain your answer.

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https://brainmass.com/chemistry/spectrum-analysis/spectroscopy-questions-165067

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Assorted infrared and nuclear magnetic resonance spectroscopy questions are answered with full working.

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Optical Spectroscopy: Grating Equation, angular seperation for different colours.

This question is about the dispersion of light when passes trough a grating. the student asked for an illustration of angular seperation between two colours.

1. The grating equation tells you at what angles different colors of light will appear:
d sin = m

where d is the separation between the lines on the grating,
m is an integer (i.e., m = 0, 1, 2, 3, etc.) known as the diffraction order number,
is the wavelength (with the same length units as d), and
is the angle at which light with wavelength is diffracted.

Make a sketch based on the figure below to show a narrow parallel beam of white light shining onto a grating with line separation d = 1000 nm. Show the angles for red and blue light for
m = 0, +1, and -1 by drawing them in appropriate colors.

Answer: we can assume that the wavelength corresponding to blue is 450 nm and for blue let it be 650 nm.
For a given value of m, according to the equation given in the question
d sin = m
,
If , , which corresponds to , This is true for both Blue and red colour. So the re is no dispersion occurs.
For ( First order spectra)

, let , where , the angle corresponds to blue and is the angle corresponding to red.
By substituting the value of , for red and for blue. Substituting the values in the equation

Fom that =26.74 degree( right side of the normal line )
, degree(( right side of the normal line )

For the , we can write =-26.74 degree( left side of the normal line ) and ( left side of the normal line ).
The figure follows.

Please note that in the figure, I just shown the angular separation.

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