The following table lists the pka of compounds we commonly use in class.

Important pKa values to know for Organic Chemistry

Alkanes		51
Amines		33-35
Alcohols		15-19
Water		15.7
Carboxylic acids		3-5
Mineral Acids	HBr HCl	-9 -7

In addition to knowing the pKa’s of Brønsted acids, Lewis acids are important.

Shown on the left is the BF3 molecule. With three bonds to fluorine (sp2 hybridization), and no lone pairs, there remains one 2p-orbital that is not hybridized and empty. Thus the boron atom needs a lone pair of electrons to give it an octet of electrons. Also, fluorine is highly electronegative, withdrawing electron density from the boron atom. This is represented in the electrostatic potential model at the upper-left, with flourine atoms in yellow-orange (partial negative charge) and boron in blue (partial positive charge). For all these reasons, the molecule BF3 is a good acceptor of electrons and therefore a good Lewis acid. Ammonia (NH3), shown in the middle, has a lone pair of electrons, and since nitrogen is more electronegative than hydrogen, the nitrogen atom has a partial negative charge (red color). In this diagram, NH3 acts as a Lewis base,when it donates its lone pair of electrons to BF3. BF3 acts as a Lewis acid when it accepts the lone pair of electrons that NH3 donates. This reaction fills BF3's empty 2p-orbital, and now boron is sp3 hybridized when previously (as BF3) it was sp2 hybridized. Note the negative charge on the boron half of the molecule (red color) and positive charge on the ammonia half of the molecule (blue color)