Propose a molecular formula for a compound that exhibits the following peaks in

Question

Propose a molecular formula for a compound that exhibits the following peaks in its mass spectrum: (a) (M)^+middot at m/z = 72, relative height = 38.3% of base peak (M+1)^+ middot at m/z = 73, relative height = 1.7% of base peak (b) (M)^+ middot at m/z= 68, relative height = 100% (base peak) (M+1)^+ middot at m/z = 69, relative height = 4.3% (c) (M)^middot at m/z = 54, relative height = 100% (base peak) (M+1)^+ middot at m/z = 55, relative height = 4.6% (d) (Mp^+ middot at m/z = 96, relative height = 19.0% of base peak (M+1)^+ middot at m/z = 97, relative height = 1.5% of base peak

Explanation / Answer

1) (M+.) m/z = 72 and (M+1) m/z = 73.

Molecular ion peak at 72 suggest molecularw eight = 72.

And weak M+1 peak suggest no other elment than C and H.

Let us find hydrocarbon structure by rule of 13.

Rule of 13: Divide molecular weight by 13 then the quotient is number of C atoms and quotient + remainder is H number and then we write hydrocarbon fomula.

Here M = 72.

On 72 / 13 we get, quotient = 5 and remainder = 7.

Hence, Number of C = 5 and number of H = 5 + 7 = 12.

Hence molecular formula is C5H12.

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2)

(M+.) m/z = 72 and (M+1) m/z = 73.

Molecular ion peak at 72 suggest molecularw eight = 72.

And weak M+1 peak suggest no other elment than C and H.

Let us find hydrocarbon structure by rule of 13.

Rule of 13: Divide molecular weight by 13 then the quotient is number of C atoms and quotient + remainder is H number and then we write hydrocarbon fomula.

Here M = 72.

On 72 / 13 we get, quotient = 5 and remainder = 7.

Hence, Number of C = 5 and number of H = 5 + 7 = 12.

Hence molecular formula is C5H12.

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2) (M+.) m/z = 68 and (M+1) m/z = 69.

Molecular ion peak at 68 suggest molecularw eight = 68.

And weak M+1 peak suggest no other elment than C and H.

Let us find hydrocarbon structure by rule of 13..

Here M = 68

On 68 / 13 we get, quotient = 5 and remainder = 3.

Hence, Number of C = 5 and number of H = 5 + 3 = 8.

Hence molecular formula is C5H8.

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3) (M+.) m/z = 54 and (M+1) m/z = 55.

Molecular ion peak at 54 suggest molecularw eight = 55.

And weak M+1 peak suggest no other elment than C and H.

Let us find hydrocarbon structure by rule of 13..

Here M = 54

On 54 / 13 we get, quotient = 4 and remainder = 2.

Hence, Number of C = 4 and number of H = 4 + 2 = 6.

Hence molecular formula is C4H6.

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4) (M+.) m/z = 96 and (M+1) m/z = 97.

Molecular ion peak at 96 suggest molecularw eight = 96.

And weak M+1 peak suggest no other elment than C and H.

Let us find hydrocarbon structure by rule of 13..

Here M = 96

On 96 / 13 we get, quotient = 7 and remainder = 5.

Hence, Number of C = 7 and number of H = 7 + 5 = 12.

Hence molecular formula is C7H12.

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