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[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 equations, derived from the acidity constant and basicity constant, states that when pH equals the pK a or pK b value of the indicator, both species are present in a 1:1 ratio. If pH is above the p K a or p K b value, the concentration of the conjugate base is greater than the concentration of the acid, and the color associated with the ...
As the name suggests, a non-nucleophilic base is a sterically hindered organic base that is a poor nucleophile.Normal bases are also nucleophiles, but often chemists seek the proton-removing ability of a base without any other functions.
The most common Lewis bases are anions. The strength of Lewis basicity correlates with the pK a of the parent acid: acids with high pK a 's give good Lewis bases. As usual, a weaker acid has a stronger conjugate base. Examples of Lewis bases based on the general definition of electron pair donor include: simple anions, such as H − and F −
The pH-dependence of the activity displayed by enzymes and the pH-dependence of protein stability, for example, are properties that are determined by the pK a values of amino acid side chains. The p K a values of an amino acid side chain in solution is typically inferred from the p K a values of model compounds (compounds that are similar to ...
This trend contrasts with the fact that Si is far less electronegative than carbon (1.90 vs 2.55, respectively). For Et 3 SiOH, the p K a is estimated at 13.6 vs. 19 for tert -butyl alcohol . The p K a of 3−ClC 6 H 4 )Si(CH 3 ) 2 OH is 11. [ 3 ]
In general, in a group across the periodic table, the more basic the ion (the higher the pK a of the conjugate acid) the more reactive it is as a nucleophile. Within a series of nucleophiles with the same attacking element (e.g. oxygen), the order of nucleophilicity will follow basicity.
These properties recommend DBU for use as a catalyst, for example as a curing agent for epoxy resins and polyurethane. It is used in the separation of fullerenes in conjunction with trimethylbenzene. It reacts with C 70 and higher fullerenes, but not with C 60. It is useful for dehydrohalogenations. [7]