Question

Give the structure that corresponds to the following molecular formula and 1H NMR spectrum: C5H10: ? 1.5, s

Answer 1

From the empirical formula, you can calculate the double bond equivalents;

http://en.wikipedia.org/wiki/Double_bond…

The compound has one double bond equivalent - that is, one double bond or a ring structure; as there is only one chemical shift, all hydrogen atoms have to be equivalent, so the structure that comes to mind is cyclopentane; if the ring is dynamic enough, i.e. at higher temperatures - room temperature may be sufficient - the signal appears as a singlet, as is observed in the spectrum (see link below for a spectrum of cyclopentane in CDCl3, taken from http://riodb01.ibase.aist.go.jp/sdbs/cgi… :

http://riodb01.ibase.aist.go.jp/sdbs/cgi…

Answer 2

I haven't taken organic chemistry in 2 months, so I hope I still remember!

Since the H1 NMR says that all of them are singlets and we have C5H10, there must be no two adjacent hydrogens that will allow for different resonances.

The molecule is therefore most likely a cyclic ring because it is symmetric, giving only one type of resonating hydrogen. If it was an alkane chain, we would need 12 hydrogens, which is not the case. Alternatively, we could add one double bond, but that would change the resonance of the hydrogen.

Answer 3

Molecular Formula : C7H16O ____ [ CnH2n+2O ] ----> Acyclic Saturated Compound ----> Alcohol _ or _ Ether


H-NMR Spectrum :

Singlet at ~ 1.38 ppm ; Area 1275 ; Disappear after Shaking with D2O ----> 1 Proton ; " acidic " proton - exchangable with D from D2O ; No Peak Splitting ( No Proton at Adjacent Carbon ) ----> Proton at -OH Group of Tertiary Alcohol

Quartet at ~ 1.42 ppm ; Area 7473 ----> 6 Identical Protons ; Located closer to Alcohol Group ; Peak Splitting by 3 Protons at Adjacent Carbon ----> [ Carbon with no H -- CH2 -- Methyl Group ] ----> 3 Identical -CH2- Groups

Triplet at ~ 0.9 ppm ; Area 11238 ----> 9 Identical Protons ; Located far away from Alcohol Group Peak Splitting by 2 Protons at Adjacent Carbon ----> [ -- Carbon with 2 H -- CH3 ] ----> 3 Identical -CH3 Groups


Conclusions :

Tertiary Alcohol
[ One -OH Group ]

Three ( 3 ) Identical -CH2-CH3 Groups attached to Tertiary Carbon
[ Three -CH2- ( 6 Protons ) ; Three -CH3 ( 9 Protons ) ]

Structure ____ ( CH3CH2 )3C-OH

IUPAC Name ____ 3-Ethyl-3-pentanol