Since you are looking to determine a structure, I presume you believe it is an unknown compound?

Eugenol had been found in this plant : http://www.ncbi.nlm.nih.gov/pubmed/16170979

If you believe the compound is unknown, you will have to purify the active compound from the extract. I like to use a column screen, where a chain gradients from weak to strong eluting solvents. This allows me to find which column might work best and also determine what sort of solvents will elute an unknown compound. Other people start by placing the extracted material into hexane, filtering, and placing the solid into ethyl acetate, and progressing to more polar solvents such as ethyl acetate, methanol, and water.

Look to see what other compounds this plant has produced, and what bio activity these compounds possess. Also look up the bio activity you are studying to see if there is a particular class, such as alkaloids, that exhibits activity. you can see how these were purified.

Links to column screening techniques:

http://www.isco.com/WebProductFiles/Applications/101/Poster_and_Paper_Reprints/New_Techniques_In_Extraction_Column_Screening.pdf

https://www.researchgate.net/file.PostFileLoader.html?id=5632181661432505f88b4575&assetKey=AS%3A289939448188930%401446138359951

Thank Jack

I think you can go for C-NMR and P+-NMR............. and then go for HPLC to isolate that compound

You can't determine the structure of an extract. You must to separate the compounds is there in. As you have and hydro alcoholic extract I think you should try a sequential partition using hexane and dichloromethane, and each one separate the chemical constituents and purify them before to determine the chemical structure using spectroscopy methods. Are you sure you want to determine the structure of all the components?. I recommend you to try at first the bioassays and then isolate the compounds from the active extract or fraction otherwise it will take long time.