A nucleophile is a chemical species that donates an electron pair to an electrophile. A nucleophile can also be called a base when this donation occurs towards a particular electrophile, which is an hydrogen ion a proton. When the size of a negatively charged molecule is small then it behaves as a nucleophile, but when size of a negatively charged molecule is big then it behaves as a base.
This is because of crowding around the central atom of other reactant species. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. What's the difference between a nucleophile and a base?
Ask Question. Asked 6 years, 11 months ago. Active 4 years, 8 months ago. Viewed 63k times. Improve this question. RobChem RobChem 9, 29 29 gold badges 73 73 silver badges bronze badges. All nucleophiles are Lewis bases; they donate a lone pair of electrons. Nucleophilicity : nucleophile attacks any atom other than hydrogen. So how do reactions of nucleophiles at hydrogen differ from reactions of nucleophiles at carbon? We can measure acidity and, by extension, basicity through the measure known as pKa, which is a reflection of the position of the equilibrium between an acid and its conjugate base.
Because we can measure the equilibrium constants for reversible acid-base reactions, we can get a fairly good idea of the relative strengths of acids and bases. The bottom line is that the more unstable a lone pair of electrons is, the more basic it will be and vice versa. How is nucleophilicity different from basicity? Many reactions of nucleophiles are not reversible. Well, we use the next best measurement available: to measure reaction rates.
There are a few more variables at play here. Factor 1: Steric hindrance. Reactions where nucleophiles attack carbon-based electrophiles are significantly more sensitive to steric effects, because empty orbitals on carbon are not as accessible.
Steric hindrance is like a fat goalie. Factor 2: Solvents. The medium solvent in which a reaction takes place can greatly affect the rate of a reaction. Specifically, the solvent can greatly attenuate reduce the nucleophilicity of some Lewis bases through hydrogen bonding. Another great question! Acid-base reactions tend to be fast , relatively speaking. But it will greatly depend on the situation. More soon, I assure you. Thank you for all great resources.
Good question. Lewis acidity is essentially electrophilicity. Acidity Bronsted acidity is what we call it when the electrophile is a proton. What is the link between being too basic and the hydride in NaH not being able to carry out the nucleophilic attack?
Thank you. NaH is generally not observed to add to aldehydes and ketones, although it will add to Lewis acids such as borane BH3. You can think about the rates of competing reactions — 1 addition of hydride to aldehyde slow versus 2 deprotonation of the alpha-carbon by hydride fast and the latter reaction prevails.
NaH acts as a non nucleophilic base so basically involves in deprotonation rather in addition of the hydride to the carbonyl. In general all non nucleophilic base acts by the same mechanism. The best guide to basicity is by looking at a pKa table. The pka of water is This was not a clear cut example where one could point to periodic trends. However with nitrogen being coordinated to C in -CN using that principle, they would draw the wrong conclusion.
Because multiple variables are in play [we are changing the basic atom as well as the substituents connected to that atom] the only recourse is to check a pKa table because the effect of changing two variables at once is not easily predictable. For example, if the nucleophilicity is high, then a certain reaction can occur fast, and if the nucleophilicity is low, the reaction rate is slow.
Since nucleophiles donate electrons, according to the Lewis definition, they are bases. The major difference between base and nucleophile lies upon their function. The bases are hydrogen acceptors which can perform neutralizing reactions whereas nucleophiles attack electrophiles to initiate some certain organic reactions. Hence, this is the key difference between base and nucleophile. Moreover, bases act as hydrogen acceptors which can perform neutralizing reactions while nucleophiles attack electrophiles to initiate some certain organic reactions.
As another important difference between base and nucleophile, we can take the type of chemical reactions that they involve in; bases involve in acid neutralizing reactions while nucleophiles involve in nucleophilic reactions. Furthermore, bases have a kinetic chemical nature which means, they react depending on the exposure it depends on. However, nucleophiles have a thermodynamic chemical nature which means they are affected by the other chemical reactions within the environment.
Every nucleophile is a base, but all the bases are not nucleophiles. Britannica, The Editors of Encyclopaedia. Available here 2. Available here. With a mind rooted firmly to basic principals of chemistry and passion for ever evolving field of industrial chemistry, she is keenly interested to be a true companion for those who seek knowledge in the subject of chemistry. Your email address will not be published. Comments which will leave substrate easily.
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