Insights from COSY Experiments

Question 1

The aromatic rings comprises of pi bonds absorbing UV lights. Thus compound 1 is not aromatic.

The functional group satisfying the conditions given is that of an aliphatic compound. It can be C = O, O - H, N - H, C - O

From the COSY experiment, the result is two-dimensional spectrum which shows single isotope frequencies and along both axes is the hydrogen (1H). The heteronuclear correlation spectra is also devised where different isotopes such as 1H and 13C corresponds the two axes. The other functional groups that can be suggested here are methine, methylene, and methyl (Dean, 1999).

The suggested structure of compound 1 is methyl ester, 4-dimethylpentanoic acid, 5-chloro-2 with 178 molecular mass and the retention time of 14.25 minutes (Dean, 1999).

Question 2

COSY spectrum

There is transfer of magnetization by scalar coupling in the COSY experiment. Protons that are apart by over three chemical bonds do not give cross signal as 4J coupling constants have closeness to 0. Thus, only protons signals that are apart by two or three bonds have visibility in COSY spectrum (red signals). Between HN and Halpha protons, the cross signals have special importance as the protein backbone’s phi torsion angle is derivable from 3J coupling that between them is constant.

NOESY Spectrum

The NOESY experiment has been vital to determine the protein structure. The spin’s dipolar interaction is used by it to correlate the protons. The NOE’s intensity is proportional to 1/r6 in the first approximation with r between the protons being the distance. Between the two

protons is the correlation depending on the distance between the two, although generally the observation of a signal is only if their distance is lower than 5 Å. All protons are correlated by the NOESY experiment that is close enough.

HMBC and HSQC are the two crucial spectra for the determination of organic structure by two-dimensional NMR. The HSQC sequence have minimized or eliminated this sequence’s earlier weaknesses that leads to over twice the increase in signal noise especially for the

edited HSQC spectra. HMBC, on the other hand, impacts the sequence’s recent modification in much lesser extent compared to the HSQC. However, the choice of processing parameters and acquisition on signal/noise of HMBC spectra can have dramatic effect.

The key differences between the reverse and the normal phase chromatography is that normal phase chromatography has a non-polar mobile phase and a very polar stationary phase, where reverse phase chromatography a polar mobile phase and non-polar stationary phase (Jandera, 2002).

Moreover, the normal phase chromatography’s stationary phase is primarily pure silica, and non-aqueous solvent is characterized in mobile phase such as chloroform while the reverse phase chromatography is long hydrophobic chains with silica substrate and mobile phase is mostly acetonitrile, methanol or water.

The reversed phase will be used to separate the compound given. Solute molecules partition between the stationary phase and mobile phase establishes the equilibrium. HPLC’s reversed phase separates successfully of both non-polar and polar neutral molecules which have below 2000 Daltons of molecular weight.

References

Dean, J. A. (1999) Lange’s Handbook of Chemistry [15th Ed], McGraw Hill Inc.

Jandera, P. (2002) ‘COMPARISON OF REVERSED-PHASE AND NORMAL-PHASE COLUMN LIQUID CHROMATOGRAPHIC TECHNIQUES FOR THE SEPARATION OF LOW AND HIGH MOLECULAR WEIGHT COMPOUNDS’, Journal of Liquid Chromatography & Related Technologies, 25:19, 2901-2931.