Question

4. Lactate is an important metabolite in cellular metabolism in health and disease. Its molecular formula is CH3CH(OH)COO^-, as seen in the figure below.

The scalar coupling between protons A and B in the figure is 7Hz. The chemical shift of one of the proton groups is 4.1ppm and that the other is 1.3ppm.

1. Assuming that the hydroxyl proton (the OH group) does not contribute to the spectrum (fast exchange with H2O protons), draw a schematic spectrum of the lactate ion and explain its features: assign correctly the chemical shift to the proton group, assess the splitting pattern, and draw it approximately in scale with respect to the expected relative amplitudes of the various peaks. Add a short verbal explanation of the spectral features.
2. If the field in which the experiment is performed is doubled, what would happen to the ratio between the splitting of the peaks within each resonance, and the chemical shift difference between the two resonances? Explain.

Answer 1

Date Structure: c ch 'H NMR 4.1 ppm Peak at 4.1 ppm indicare a strong elecko- negative atom is present neighbouring to с-и точр, Peak at 1.3 ppm indicate a shielding protons. Hose _CH₂ protons are shielded as compained with - cm protons so 4.1 ppm value is for C-H group & 1.3 ppm voque is for the group This peak show's 3 times amplitude to that of 4.18 1.3ppm (doubler, 34). peak. & 4.10 ppm (quarter, 1H). - CH₂ 1.38( doublet) HC 4.1 ppm (quartet) multiplicity is according to ntl rue. Amplitude ratio of 4.18 to 138 is 1:3 . If the field is doubled there is no any change occure on the ratio between the splitting of the peaks & Chemical shift. Chemical shift is measured in ppm. = VH-VTMS x 10 ppm. VNMR