Question

Can you explain these questions with full working out and answers please. Also, what does m/z 72 molecular ion mean in this question? Thank you!

Elemental analysis of an unknown compound reveals that it oontains (pnly) the elements C, H& O, and that it contains 66.6 % carbon and 11.2 % hydrogen by mass. The mass spectrum of this compaund contains a molecular ion signal at m/z 72. The IR spectrum of this compound contal ns a strong signal at 1715 cm. The 1H NMR apectrum of this compound is shown below. Integretion 2 Intearation 3 Integration 3 pPM 1. What is the malecular formula of this compound? al CHo e CaH4Oz 2. What is the index of hydrogen deficiency HD)? a) ici 2 i3 1715 cm1? 3, What kind of bond ia likely reaponelble for IR signela A) C-H ib) C-O (c) C-o iei C-C 4. How many hydrogen environments exist in this compound? (3 (el 4 6. What is the likely structure of this compound? C a) el (e) (a el int (el

Answer 1

1. Answer is option (b) C₄H₈O

Explanation:

Consider 100 g of unknown compound

Then 66.6 g of carbon, 11.2 g of hydrogen and 22.2 g of oxygen

To get moles of carbon, hydrogen and oxygen divide by atomic weight

C = 66.6 / 12 = 5.55; H = 11.2 / 1.008 = 11.11; 22.2 / 16 = 1.38

To get formula divide by smallest number

No. of carbon = 5.55 / 1.38 = 4

No. of hydrogen = 11.11 / 1.008 = 8.05

No. of oxygen = 1.38 / 1.38 = 1

Therefor formula = C₄H₈O

2.

Answer is option (b) = 1

Explanation:

Formula = C-H/2+1

Where C = no. of carbon; H = no. of hydrogen

4 – 8/2 + 1 = 1

3.

Answer is option (c) = C=O

Explanation: the band at 1715 cm-1 is for carbonyl stretching frequency

4.

Answer is option c: 3

Explanation:

singlet at 2.1 ppm for methyl group attached to carbonyl group

Quartet at 2.5 ppm for CH2 attached to carbonyl group

Triplet at 1 ppm is for for CH3 group attached to CH2 group

5.

Answer is option e.

CH3 Н,с

Explanation:

singlet at 2.1 ppm for methyl group attached to carbonyl group

Quartet at 2.5 ppm for CH2 attached to carbonyl group

Triplet at 1 ppm is for for CH3 group attached to CH2 group