[jimbowak]

I have an unknown which I've narrowed down to either pentane or hexane. It is most likely hexane (from refractive index) but i need to be able to explain it with H-NMR data (below).

CH3-CH2-CH2-CH2-CH3
(3)    (2)   (1)
CH3-CH2-CH2-CH2-CH2-CH3

delta   pattern   integ   multiplicity
0.89   t   2.53   t
0.89   t   2.53   t
1.23   tt   2.00   t
1.23   tt   2.00   t
1.27   h   2.95   h
1.27   h   2.95   h

Both have POS (pent is split on a carbon vs hex is split at a bond) so they would both show 3 distinct hydrogens. How do i explain that the integration is hexane and not pentane?

sincerely
James

[sjb]

I have an unknown which I've narrowed down to either pentane or hexane. It is most likely hexane (from refractive index) but i need to be able to explain it with H-NMR data (below).

CH3-CH2-CH2-CH2-CH3
(3)    (2)   (1)
CH3-CH2-CH2-CH2-CH2-CH3

delta   pattern   integ   multiplicity
0.89   t   2.53   t
0.89   t   2.53   t
1.23   tt   2.00   t
1.23   tt   2.00   t
1.27   h   2.95   h
1.27   h   2.95   h

Both have POS (pent is split on a carbon vs hex is split at a bond) so they would both show 3 distinct hydrogens. How do i explain that the integration is hexane and not pentane?

sincerely
James

What does your "pattern" notation mean - how is it different to "multiplicity"? I'm a bit confused as you seem to have listed peaks twice with the same delta?

[jimbowak]

I was hoping somebody could tell me that. lol. This is what we are given with very little explanation. Still at a standstill for explaining why this is hexane and not pentane.

[gfunk]

A wild guess would be pattern = second-order splitting and multiplicity = first-order splitting.  Anyhow, why does the integration add up to 15 protons?  Either the 1H-NMR spectrum was poorly integrated (should try to integrate total peaks instead) or there's a nitrogen in there (yielding an odd number of protons).  Are you certain it can only be either pentane or hexane?

[jimbowak]

reasonably certain. solubility showed that it was inert. all functionaly group testing came up negative. Refractive index in between pentane and hexane. I brought it to my prof, he saw that i had drawn hexane on the graph. he said "ah, that's it." and pointed at the integration data. I was just at a loss to explain it given the 15 protons. It's off to be marked already so we'll see.

[Dolphinsiu]

For hexane, the ratio of integration number of protons are 4:4:6 = 2:2:3

Foir pentane, the ratio of integration number of protons are 2:4:6 = 1:2:3

Actually from your given integration number, 2.53 is somewhere between 2 and 3...so it seems this explaination becomes invalid.

For multiplicity and proton chemical shift:

For hexane,

0.89   4H    quintet
1.23   4H    sextet (triplet of triplet)
1.27   6H    triplet

Also multiplicity cannot explain the existence of hexane structure.....Are you sure that you give correct information?