# Provide a structure for the following compound: molecular mass 71; IR: 3200 (strong, broad), 2250 cm–1; no abs?

0

I know it’ll have a C-C(triple bond) with an -OH or secondary -NH2 but i dont know how to set it up

### 2 Answers

• According to the nitrogen rule, the mass of 71 would indicate an odd number of nitrogens (1, 3 …). If we consider that the IR absorption at 3200 (strong, broad) is NH2 (mass = 16), then we can figure out a putative molecular formula:

71 – 16 = 55

57/12 = 4.58; therefore, we consider that there are 4 carbons present.

55 – 48 = 7

Thus would indicate that there are 7 hydrogens present, so the putative molecular formula is

C4H9N

or C4H7NH2

It appears that your question was cut off, so probably there is additional information that would be of use to us to narrow down th possible structures.

• I am afraid Doctorwho does not have the answer. However, the user also did not give all the information needed to complete this problem…

First we know for a fact there is a nitrogen in there since the molecular mass is odd.

we also know that a broad band at 3200 signifies a NH or an OH, we will come back to this. A strong broad band at 2250 is a good indicator of a nitrile group.

What was left out was the 2 signals on the nmr at roughly 240. These signals are both for 2H and have tertiary multiplicity. This means you have two CH2 groups that have 2 hydrogen neighbors. To me this indicates that the CH2s are neighbors.

Combine the two CH2 and the nitrile – The molecular weight adds up to 55

71-55=16

Now we come back to the broad peak at 3200, we know it is either an OH or NH.

OH weight= 16

NH weight= 15

OH is the only one that adds to 71, add the OH to the other CH2 and you get:

N:::C:CH2:CH2:OH

Colons signal bonds

Also Check This  Ap classroom unit 3 progress check mcq answers