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Khan Academy
Khan Academy: Chemistry: Molecular and Empirical Formulas
A video lecture explaining how to find the molecular and empirical formula knowing the percent composition of each element. The problem is solved in easy to follow steps. [9:30]
Khan Academy
Khan Academy: Organic Chemistry: Spectroscopy: Proton Nmr: Hydrogen Deficiency Index
How to relate molecular structure with the molecular formula using the hydrogen deficiency index (or number of degrees of unsaturation). [8:50]