Question

number 2

Relevant i = 12 nuclei and relative natural abundances are as follows (assume all other nuclei are spin inactive): 19F (1 = /2, 100%) TH (1 = 12, 100%) 295i (1 = 42, 4.7%) 31P (1 = /2, 100%) 77 Se (1 = 12, 7.6%) Also, assume 1 > 2/> 34, there is no resolvable 4 coupling, and there is no observable coupling to 13C nuclei. 1. Using stick diagrams, sketch the TH NMR spectra for the following compounds. Assume structures are rigid in solution (give all isomers). Include all relative peak intensities and label all couplings. a) PBrzMe b) AsFMe2 c) SeMe2 d) PF Me e) SbCI(CH2CH3)2 2. Using stick diagrams, sketch the 31P NMR spectra for the following compounds. Assume structures are rigid in solution (give all isomers). Include all relative peak intensities and label all couplings. a) MezP-SiMe3 (1H decoupled) b) PF4CI c) H2P(CF3) d) PF5 e) P(CF3)3

Answer 1

Question 2.

a) Doublet will appear

Explanation: Phosphorus couples with ²⁹Si, multiplicity of the signal = 2nI + 1 = 2*1*1/2 + 1 = 2 (doublet).

b) Quartet of doublet will appear

Explanation: Phosphorus first couples with equatorial ¹⁹F, multiplicity of the signal = 2nI + 1 = 2*3*1/2 + 1 = 4 (quartet), followed by coupling with axial¹⁹F, multiplicity of the signal = 2nI + 1 = 2*1*1/2 + 1 = 2 (doublet). Hence, each line of the quartet will further split into doublet, i.e. quartet of doublet.

c) Quartet of triplet will appear

Explanation: Phosphorus first couples with equatorial ¹⁹F, multiplicity of the signal = 2nI + 1 = 2*3*1/2 + 1 = 4 (quartet), followed by coupling with ¹H, multiplicity of the signal = 2nI + 1 = 2*2*1/2 + 1 = 3 (triplet). Hence, each line of the quartet will further split into triplet, i.e. quartet of triplet.

d) Sextet (at room temperature); quartet of triplet (at low temperature) will appear.

Explanation: At room temperature, all the five F's undergo rapid exchange from axial to equatorial, hence the multiplicity of the signal = 2nI + 1 = 2*5*1/2 + 1 = 6 (sextet). At low temperature such as -78^oC,  phosporus first couple with equatorial ¹⁹F, multiplicity of the signal = 2nI + 1 = 2*3*1/2 + 1 = 3 (quartet), followed by coupling with axial ¹⁹F, multiplicity of the signal = 2nI + 1 = 2*2*1/2 + 1 = 3 (triplet). Hence, each line of the quartet will further split into triplet, i.e. quartet of triplet.

e) Dectet will appear.

Explanation: Phosphorus couples with ¹⁹F, multiplicity of the signal = 2nI + 1 = 2*9*1/2 + 1 = 10 (dectet).