A certain compound has the following elemental analysis (percent composition by

Question

A certain compound has the following elemental analysis (percent composition by mass), where “X” is an unknown element (N, O, Cl, or Br): % C 74.93; % H 12.59; % X 12.48 Its IR spectrum and mass spectrum are given below. Answer the questions on the next page. While you do not need to fully analyze all of this data or determine the exact structure, you may wish to use different spectral details to help determine certain functional groups or other substructures.
a. What element is element X? Explain your reasoning briefly. b. Calculate the empirical formula of this compound. Remember to include all your work. c. Write the mass of the molecular ion (M+ signal of mass spectrum). d. Calculate the molecular formula of the compound. e. Write the mass of the base peak as seen on the mass spectrum f. What structural fragment(s) were lost from the molecular ion to give the peak whose relative intensity is approximately 70 on the mass spectrum? You may wish to figure out a subset of the molecular formula itself that represents the lost mass, and then figure out some simple alkyl(s) or other group(s) that could give that total formula.

a. What element is element X? Explain your reasoning briefly. b. Calculate the empirical formula of this compound. Remember to include all your work. c. Write the mass of the molecular ion (M+ signal of mass spectrum). d. Calculate the molecular formula of the compound. e. Write the mass of the base peak as seen on the mass spectrum f. What structural fragment(s) were lost from the molecular ion to give the peak whose relative intensity is approximately 70 on the mass spectrum? You may wish to figure out a subset of the molecular formula itself that represents the lost mass, and then figure out some simple alkyl(s) or other group(s) that could give that total formula.

L00 50 4000 AVENU8ERI 500 100 80 40- 20 0 25 50 75 100 125

Explanation / Answer

The element “X” will be Nitrogen.

Assume 100 g of the unknown compound is there. In this

74.93 g of Carbon, 12.59 g of hydrogen and 12.48 g of X

First convert the mass of C nad H to moles

C = 74.93 / 12 = 6.24

H = 12.59 / 1 = 12.59

If X considered as Nitrogen then

N = 12.48 / 14 = 0.89

To get the whole number we have to divide the values by the lowest value.

C = 6.28 / 0.89 = 7

H = 12.59 / 0.89 = 14

N = 0.89 / 0.89 = 1

So the formula is C7H14N

So the molecular weight calculation it is found that

(7x12) + (14x1) + (1x14) = 112

From the mass spectra, it is shown that the M+ ion peak is 113

So this will be the compound.

(Like wise you calculate for O, Cl, Br. It will not match the mass value.

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