Question

Analzye the following spectra, and propose a structure for each. The bottom set of 3 spectra are DEPT spectra, top: CH only, middle: CH, CH3 up, CH2 down, bottom: normal BB decoupled spectrum. Explain your assignments . Analyze means determine integrals, draw splitting trees, determine carbon type (C, vs CH vs CH2 vs CH3 and structural environment. Use ChemDraw to check your proposed structure (include output),

Problem C 7.5 7.0 .5 6.05.55.0 4.5 4.03.5 3.0 2.5 ppm 31 ppm 140 130 120 110 100 908070 60 50 40 30 20 10 ppm

Answer 1

ANSWER: To propose the structure from the given NMR data,

1. Analyze the ¹H-NMR data for the nature of the hydrogens in the compound with the help of chemical shift values and peak multiplicities.
2. Interpret the ¹³C-NMR broadband spectrum for the nature of carbons.
3. And also remember that DEPT-90 will show positive peaks only for -CH groups & DEPT-135 will show positive (upward) peaks for -CH/-CH₃ groups and negative (downward) peaks for -CH₂ group.

Based on the above data, the most probable structure is given below.

The Щ-NMR spectrum interpretation was done and formulated in the table Hydrogen Chemical shift label Interpretation/possible fragment responsible for the chemical shift pm)/ Multiplici 2.30 ppm/singlet Ha | These protons may belong methyl group which is attached to a benzene ring Ho & 7.05 ppm/doublet 8 7.40 ppm/doublet to a 1,4-disubstituted benzene ring | These protons may belong to aromatic protons in specific i.e.) 1,4-disubstituted benzene rin * The 13C-NMR spectrum is suggesting the follows Appearance of five peaks in the spectrum suggesting that the compound has five non-equivalent carbon atoms The peak appeared at δ 137.0 ppm belong to the aromatic tertiary carbon which might be attached to a more electronegative atom (carbon doesn't have any hydrogens, peak in DEPT-90 & DEPT The peak appeared at δ 131.2 & 130.8 ppm belong to the aromatic carbon which is attached to a The peak appeared at 8 119.0 ppm belong to the aromatic tertiary carbon (carbon which didn't The peak appeared at δ 21.0 ppm belong to the-CH3 carbon (peak is positive in DEPT-90 & DEPT 135 absent). hydrogen atom (peaks are positive in DEPT-90 & DEPT-135). attached to any hydrogens, peak in DEPT-90 & DEPT-135 absent) 135) With the help of the above data, the most appropriate structure is determined as 4-bromo to ulene CH 4-bromo toulene (a, b, c are the hydrogen labels showed in the table)