Try links below as introduction:

http://www.claessen.net/chemistry/base_en.html

http://www.liv.ac.uk/Chemistry/Links/links.html

I have many links to collections of chemistry related websites, but last time use direct search by Google and sometimes by other search engines. This need some training in formulation of "keywords cloud", but is more productive in long-range perspective.

Try these links

http://www.chemspider.com/

ChemSpider is freely accessible and has reliable database. To search in it one need either the CAS no. or the smile codes of the chemical

Also one can use HSDB too for more information about the toxicological data.

http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB