Mechanism of the addition of HX to alkynes involves the intermediacy of the vinylic carbocation

1. Every Brønsted-Lowry acid has a conjugate base; every Brønsted-Lowry base has a conjugate acid. 2. Brønsted-Lowry acids and bases can be neutral species, cations, or anions. 3. A Brønsted-Lowry base must contain at least one lone pair of electrons to form a bond with H +, which has no electrons of its own. 5. The stronger acid reacts with the stronger base to form a weaker acid and a weaker base. 6. The stronger the acid, the weaker its conjugate base, and vice versa. 7. Neither H + (aq) nor H 3 O + (aq) is a true representation of the aquated proton. Both are shorthand notations and as such are used interchangeably. However, H 3 O + (aq) is far preferable!

Brønsted-Lowry Acid: Substance that can donate H + Brønsted-Lowry Base: Substance that can accept H + Chemical species whose formulas differ only by one proton are said to be conjugate acid–base pairs.

Brønsted-Lowry Acid–Base Concepts

Weak Acid Ionization Constants 7.1 x 10 –4 4.5 x 10 –4 3.0 x 10 –4 1.7 x 10 –4 8.0 x 10 –5 6.5 x 10 –5 1.8 x 10 –5 4.9 x 10 – x 10 –10 HF HNO 2 C 9 H 8 O 4 (aspirin) HCO 2 H (formic) C 6 H 8 O 6 (ascorbic) C 6 H 5 CO 2 H (benzoic) CH 3 CO 2 H (acetic) HCN C 6 H 5 OH (Phenol) F – NO 2 – C 9 H 7 O 4 – HCO 2 – C 6 H 7 O 6 – C 6 H 5 CO 2 – CH 3 CO 2 – CN – C 6 H 5 O – ACID CONJ. BASEK a pK a =-logK a

Very Weak Acid Ionization Constants CH 3 COCH 2 COCH 3 CH 3 NO 2 H 2 O C 2 H 5 OH CH 3 COCH 3 RCCH RCH=CH 2 CH 3 CH 3 COCH – COCH 3 – CH 2 NO 2 OH – C 2 H 5 O – CH 3 COCH 2 – RCC – RCH=CH – CH 3 CH 2 – ACID CONJ. BASEpK a

1. For binary acids in the same group acidity increases with increasing size of A. 2. For binary acids in the same row acidity increases with increasing electronegativity of central atom in A. 3. In most cases acidity increases as the ability of the conjugate base to disperse negative charge increases. The lower the charge- to-radius ratio of the conjugate base the more stable it is and the stronger its conjugate acid. Brønsted-Lowry Acid Strength

Oxoacids with different central atoms that are from the same group of the periodic table and that have the same oxidation number, acid strength increases with increasing electronegativity. Brønsted-Lowry Acid Strength

Oxoacids with same central atom, acid strength increases with increasing size.

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