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A plot of the common logarithm of the reaction rate constant k versus the logarithm of the ionization constant K a for a series of acids (for example a group of substituted phenols or carboxylic acids) gives a straight line with slope α and intercept C. The Brønsted equation is a free-energy relationship.
where log(k s /k CH 3) B is the ratio of the rate of the base catalyzed reaction compared to the reference reaction, log(k s /k CH 3) A is ratio of a rate of the acid catalyzed reaction compared to the reference reaction, and ρ* is a reaction constant that describes the sensitivity of the reaction series. For the definition reaction series, ρ ...
[c] [2] For example, a hypothetical weak acid having K a = 10 −5, the value of log K a is the exponent (−5), giving pK a = 5. For acetic acid, K a = 1.8 x 10 −5, so pK a is 4.7. A higher K a corresponds to a stronger acid (an acid that is more dissociated at equilibrium).
The ideal kinetic resolution is that in which only one enantiomer reacts, i.e. k R >>k S. The selectivity (s) of a kinetic resolution is related to the rate constants of the reaction of the R and S enantiomers, k R and k S respectively, by s=k R /k S, for k R >k S. This selectivity can also be referred to as the relative rates of reaction.
Catalysis (/ k ə ˈ t æ l ə s ɪ s /) is the increase in rate of a chemical reaction due to an added substance known as a catalyst [1] [2] (/ ˈ k æ t əl ɪ s t /). Catalysts are not consumed by the reaction and remain unchanged after it. [3]
In acid catalysis and base catalysis, a chemical reaction is catalyzed by an acid or a base. By Brønsted–Lowry acid–base theory, the acid is the proton (hydrogen ion, H +) donor and the base is the proton acceptor. Typical reactions catalyzed by proton transfer are esterifications and aldol reactions.
The reaction rate varies depending upon what substances are reacting. Acid/base reactions, the formation of salts, and ion exchange are usually fast reactions. When covalent bond formation takes place between the molecules and when large molecules are formed, the reactions tend to be slower.
If the reaction is first order it has the unit s −1, and for that reason it is often called the frequency factor or attempt frequency of the reaction. Most simply, k is the number of collisions that result in a reaction per second, A is the number of collisions (leading to a reaction or not) per second occurring with the proper orientation to ...