Based on the mass spectrum showa below and no other information, deduce the stru

Question

Based on the mass spectrum showa below and no other information, deduce the structure of the unknown that corresponds to the mass sp 100 3. tnim- 50 85 110 20 50 80 7080 0100 30 40 4. An unknown non-branched alkane has the mass spectrum shown below. Based on this mass spectrum and no other information, what is the structure of the unknown alkane? The mass spectrum below is said to show a "hydrocarbon cluster". Explain. 100 57 43 50 85 113 127 141 155 169 183 197 211 225 239 253 282 20 40 80 80 100 120 140 160 180 200 220 240 260 280

Explanation / Answer

Part 1) Here molecular ion peak is at 112 and there is a M+2 peak at 114. This indicates the presence of halogen.

Since the molecular ion peak and M+2 peak is in 3:1 ratio, the halogen present is Chlorine,

Therefore 112-35=77

and number of carbons = 112/12= 6 Carbons

From these data, The spectrum provided corresponds to Chlorobenzene

Part 2)

From the molecular ion peak at 282, the linear alkane is Eicosane (C20H42)

The mass spectrum here shows a hydrocarbon cluster due to the fragmentation of the parent alkane. These peaks are due to C2H5+(29), C3H7+(43), C4H9+(57), C5H11+(71), C6H13+(85) etc.

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