Thanks indu

Dear HIFSA MUBEEN

The constitutional assignment of natural products by NMR spectroscopy is usually based on 2D NMR experiments like COSY, HSQC, and HMBC. The actual difficulty of the structure elucidation problem depends more on the type of the investigated molecule than on its size. The moment HMBC data is involved in the process or a large number of heteroatoms is present, a possibility of multiple solutions fitting the same data set exists. A structure elucidation software can be used to find such alternative constitutional assignments and help in the discussion in order to find the correct solution. But this is rarely done. This article describes the use of theoretical NMR correlation data in the structure elucidation process with WEBCOCON, not for the initial constitutional assignments, but to define how well a suggested molecule could have been described by NMR correlation data. The results of this analysis can be used to decide on further steps needed to assure the correctness of the structural assignment. As first step the analysis of the deviation of carbon chemical shifts is performed, comparing chemical shifts predicted for each possible solution with the experimental data. The application of this technique to three well known compounds is shown. Using NMR correlation data alone for the description of the constitutions is not always enough, even when including 13C chemical shift prediction.

Hearty Thanks to:[email protected]

please you may contact: [email protected]

Ab initio methods for NMR spectra prediction, such as Gaussian, are presently not significantly

more accurate than database-based methods but they are slower by many orders of magnitudes.

Deciding which software is the "best" one is a matter of taste. Best for accuracy, best for the budget,

easiest to use? ChemDraw has an integrated chemical shift predictor: very easy. NMRShiftDB can freely be used

through a web interface, and even as a standalone application on your computer: no cost. Companies such as

Modgraph, Perch, ACD and others sell software that rely on huge collections of published data.

The quality and the size of database, as well as the prediction algorithm make the difference.

I recommend you the reading of "Progress in Nuclear Magnetic Resonance Spectroscopy 53 (2008) 1-104".

It is written by ACD people but also discuss other prediction systems than theirs.

ChemBioDraw Ultra / ChemDraw Ultra of Cambridge soft.

ChemNMR estimates chemical shifts for all hydrogen or carbon atoms for which additivity rules are available. Following a hierarchical list, it first identifies key substructures of a molecule. A substructure provides the base value for the estimated shift. For example, benzene would be identified as the key substructure of trinitrotoluene.

When a substructure is a ring system not available in the data, ChemNMR approximates its base shift using embedded rings and, if necessary, it will disassemble the ring into acyclic substructures.

ChemNMR views remaining parts of the molecule as substituents of a substructure. Each substituent adds to or subtracts from the base shift of the substructure to which it is attached. Additivity rules determine the increment of each contribution. If an increment for a substituent cannot be determined, ChemNMR uses embedded substituents—smaller structural units with the same neighboring atoms. Or, it will use increments of identical or embedded substituents of a corresponding substructure by assuming that the effects of the substituents are of the same magnitude.

ChemNMR provides a detailed protocol of the estimation process applied. It gives substructures as names, compound classes in most cases, substituents in form of a linear code, respectively.

The data set for the 1H NMR Shift tool currently contains 700 base values and about 2000 increments. The 13C NMR Shift tool is based on 4000 parameters. It also implements models for ethylenes (cis/trans) and cyclohexanes (equatorial/axial).

Regards

Selvan

Hi Hifsa, my answer to your questio "which software is best...for NMR":

I recommend to ACDLabs as a good source. This does not mean that it is "the best" , but certainly one of the best amongst many others.

http://www.acdlabs.com/products/adh/nmr/

Regards

Bruno

Dear Hifsa Mubeen,

Can try and submeet the optimized molecule to GIAO/SCF NMR calculations by the use of Gaussion 03/09 at DFT/B3LYP/6-31 G(d,p) level. I think it will enough.

Your regards

Dr. T. B. Pawar.

Hi, I and my colleague developed a software to search the compounds IDs from HMDB, MMCD, Metlin and LipidMaps. It support CAMERA and m/z. It might be helpful for you to predict the compounds ID. Here is the link:

http://omics.georgetown.edu/MetaboSearch.html

Dear Hifsa

Did You find your answer about NMR prediction approach and software?

SPINUS-WEB is very useful if you are looking for prediction of full proton NMR spectra.

http://www2.ccc.uni-erlangen.de/services/spinus/

Unfortunately chemdraw and mestrenova or any other software which uses their database as the main predictor can not be accurate for every structure. For example if you try to predict 1H NMR or 13 C NMR of Octa Amino Phenyl Silsesquioxane (OAPS) you get two different results with this two softwares. By comparing their outputs with experimental results one can immediately find the differences and errors. Since these softwares use their databases so the prediction results completely depend on the similarity of your designed structure with those existed in the database. Mestrenova uses HOSE ( Hierarchical Organisation of Spherical Environments ) to predict NMR. The HOSE starts at the carbon atom whose shift is to be predicted, looks one bond away from the carbon and tries to find this environment in its database. If it is successful it moves two bonds away and tries again and so on until it either comes across something not represented in the database or it reaches the boundary of the molecule.

The problem with QM programs like Gaussian is that the prediction is done in gas phase so you have to make solvent correction which is not so accurate. On the other hand accuracy also depends on the basis set used.

You can use Chemdraw to predict proton and C-13 NMR. Please watch the following video:

https://www.youtube.com/watch?v=vaZGTcpIKzc