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A polar reaction is a nucleophile giving an electron pair to an electrophile; nucleophiles have lone pairs, negative charges or pi bonds, electrophiles have positive charges, empty orbitals or δ+ atoms, and neither role depends on charge alone.
Paper packet. Every task here also exists on screen, where it is checked automatically; answers written on paper are not assessed by Nydus. When you are back at a device, enter your answers there.
You will draw which species gives an electron pair to which, sort species by role, define a nucleophile, rank nucleophiles, and name the roles in a reaction with a neutral nucleophile.
You can find a molecule's electron-rich and electron-poor sites, and you know an acid-base reaction moves a proton from one to the other. Most organic reactions follow the same pattern with carbon in place of the proton.
A nucleophile (nucleus-loving) gives a pair of electrons to form a new bond. An electrophile (electron-loving) accepts one. A Lewis base and a Lewis acid are the general names for an electron-pair donor and acceptor; a base is a nucleophile that attacks a proton.
A polar reaction forms a bond from a pair of electrons that one species had and the other lacked:
Nucleophiles have: a lone pair (H2O, NH3), a negative charge (OH−, CN−, CH3O−) or a pi bond (C=C). Electrophiles have: a positive charge (H+, CH3+), an empty orbital (BF3), or a δ+ atom (the carbon of C=O or C–Br).
The words describe electrons, not charge. Neutral water is a nucleophile; neutral propanone's carbonyl carbon is an electrophile.
Another way: steps
To name the roles:
Some nucleophiles give their pair more readily than others. A negative charge helps: hydroxide reacts far faster than water, the amide ion than ammonia. So does a less electronegative atom, which holds its pair less tightly: nitrogen nucleophiles beat the matching oxygen ones. These trends mostly follow basicity, because attacking a proton and attacking a carbon are the same act. The next lesson draws that act as a curly arrow.
A nucleophile is defined by having a positive charge. It is defined by a pair to give.
Only charged species react. Water and ethene are neutral nucleophiles.
The larger molecule is the electrophile. Electron supply decides.
The leaving group is the nucleophile. It departs; it does not attack.
The new bond is C–C, from cyanide's carbon to the carbonyl carbon.
Find the new bond.
The pair came from cyanide's lone pair, so cyanide is the nucleophile.
Whose electrons?
The δ+ carbonyl carbon received it, so propanone is the electrophile.
Rich gives to poor.
Which species has a lone pair to give?
Water.
Which has room to take it?
The methyl cation, with its empty orbital: the electrophile.
Three reactions: hydroxide reacts with bromomethane; ammonia takes a proton from the hydronium ion; cyanide adds to ethanal. Draw each with 'gives an electron pair to', from the species that gives to the one that receives.
This task has no paper form; do it on a device.
Match each species to its usual role.
| nucleophile | electrophile | |
|---|---|---|
| water, H2O | ||
| the methoxide ion, CH3O− | ||
| ethene's pi bond | ||
| the methyl cation, CH3+ | ||
| boron trifluoride, BF3 |
Which statement correctly defines a nucleophile?
Rank these from the most willing to give its electron pair to the least: ammonia, water, the amide ion NH2−, the hydroxide ion OH−.
Number the steps in order (write the number in the box):
Ethanoyl chloride, CH3COCl, reacts with water to give ethanoic acid and HCl. In the first step a new bond forms between an oxygen of water and the carbonyl carbon. Which is the nucleophile?
Lesson test: one question per skill, one attempt each, no hints. Your answers are checked when you submit.
For each reaction, name the nucleophile and the electrophile.
| nucleophile | electrophile | |
|---|---|---|
| methoxide + iodomethane | ||
| ethene + HBr | ||
| ammonia + BF3 |
You can name who gives and who takes in a polar reaction. Tell someone why water is a nucleophile. Next: the curly arrow, which records exactly where the pair goes.
8. Your turn: water with a methyl cation, step 3