versions of Alkyl Halides and Nucleophilic Substitution:
main
| yours | all (3)
Alkyl Halides and Nucleophilic Substitution
 rename
Updated
2010-05-14 18:57
General
| Statement | Missing Words |
|---|
| ___ stands for a halogen atom | X |
| Alkyl halides are often abbreviated as ___ | RX |
| Alkyl groups are often abbreviated as ___ | R |
| Nucleophiles are abbreviated _________ | :Nu- |
| Bronsted-Lowry bases are abbreviated ___ | :B |
| Alkyl halides have the general molecular formula ___ | CnH2n+1X |
| Vinyl halides have a halogen atom X bonded to ___ | a carbon-carbon double bond |
| Aryl halides have a halogen atom X bonded to ___ | a benzene ring |
| Allylic halides have a halogen atom X bonded to ___ | a carbon atom adjacent to a carbon-carbon double bond |
| Benzylic halides have a halogen atom X bonded to ___ | a carbon atom adjacent to a benzene ring |
| Vinyl and aryl halides have a halogen atom X directly bonded to ___ | an sp2 hybridized carbon atom |
| Allylic and benzylic halides have a halogen atom X directly bonded to ___ | an sp3 hybridized carbon atom |
| Alkyl halides are ___ molecules | weakly polar |
| Alkyl halides contain polar ___ bonds | C-X |
| Alkyl halides are incapable of ___ | intermolecular hydrogen bonding |
| Alkyl halides have ___ boiling points and melting points than alkanes containing the same number of carbons | higher |
| Alkyl halides with larger surface area have ___ boiling points and melting points | higher |
| Alkyl halides with less polar halogens have ___ boiling points and melting points | lower |
| Alkyl halides are soluble in ___ | organic solvents |
| Alkyl halides are insoluble in ___ | water |
| memorize |
| Statement | Missing Words |
|---|
| Alkyl halides undergo ___ reactions with nucleophiles | substitution |
| Alkyl halides undergo ___ reactions with Bronsted-Lowry bases | elimination |
| R-X + :Nu- -> R-Nu + X:- is a general ___ reaction | substitution |
| ___ contain a lone pair or a π bond but not necessarily a negative charge | nucleophiles |
| Nucleophilic substitutions are ___ reactions | Lewis acid-base |
| ___ attack protons | bases |
| ___ attack other electron-deficient atoms (usually carbons) | nucleophiles |
| A nucleophile is a ___ that reacts with electrophiles other than protons | Lewis base |
| A ___ is a base that reacts with protons | Bronsted-Lowry base |
| Nucleophiles and bases are structurally similar: both have a ___ | lone pair or a π bond |
| ___ is the systematic preparation of a compound from a readily available starting material by one or many steps | organic synthesis |
| memorize |
Leaving Groups
| Statement | Missing Words |
|---|
| In comparing two leaving groups, the better leaving group is the ___ base | weaker |
| Left-to-right across a row of the periodic table, basicity decreases so leaving group ability ___ | increases |
| Down a column of the periodic table, basicity ___ so leaving group ability increases | decreases |
| From left-to-right the leaving group ability of F-, Cl-, Br-, and I- ___ | increases |
| From left-to-right, the basicity of NH3 and H2O ___ | decreases |
| Cl-, Br-, I-, and H2O are ___ leaving groups | good |
| F-, -OH, -NH2, H-, and R- are ___ leaving groups | poor |
| Molecules with ___ leaving groups undergo nucleophilic substitution | good |
| Molecules with ___ leaving groups do not undergo nucleophilic substitution | poor |
| Equilibrium favors the products of nucleophilic substitution when the nucleophile is a ___ base than the leaving group | stronger |
| The ___ the conjugate acid, the stronger the base | weaker |
| The ___ the conjugate acid, the better the leaving group | stronger |
| The ___ the base, the better the leaving group | weaker |
| In general, ___ bases are stronger nucleophiles | stronger |
| A negatively charged nucleophile is always ___ than its conjugate acid | stronger |
| Left-to-right across a row of the periodic table, nucleophilicity ___ as basicity decreases | decreases |
| Left-to-right, the basicity of F-, -OH, -NH2, and CH3- ___ | increases |
| Steric hindrance ___ nucleophilicity but not basicity | decreases |
| Sterically hindered bases that are ___ nucleophiles are called nonnucleophilic bases | poor |
| memorize |
Solvent Effects
| Statement | Missing Words |
|---|
| ___ solvents solvate both cations and anions well | polar protic |
| ___ solvents are capable of intermolecular hydrogen bonding | polar protic |
| ___ are solvated by ion-dipole interactions | cations |
| ___ are solvated by hydrogen bonding | anions |
| ___ solvents are incapable of intermolecular hydrogen bonding | polar aprotic |
| ___ solvents solvate only cations well | polar aprotic |
| ___ solvents contain O-H or N-H bonds | polar protic |
| water, methanol, ethanol, tert-butanol, and acetic acid are ___ solvents | polar protic |
| acetone, acetonitrile, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and hexamethylphosphoramine (HMPA) are ___ solvents | polar aprotic |
| In ___ solvents, nucleophilicity rises with increasing size of an anion (opposite to basicity) | polar protic |
| memorize |
SN1 and SN2 Reactions
| Statement | Missing Words |
|---|
| In the ___ mechanism, bond breaking and bond making occur simultaneously | one-step |
| In the ___ mechanism, bond breaking occurs before bond making | two-step |
| An SN2 reaction follows the ___ mechanism | one-step |
| An SN1 reaction follows the ___ mechanism | two-step |
| ___ stands for substitution nucleophilic bimolecular | SN2 |
| ___ stands for substitution nucleophilic unimolecular | SN1 |
| An ___ reaction exhibits second-order kinetics | SN2 |
| An ___ reaction is bimolecular | SN2 |
| An ___ reaction's rate depends on the concentrations of both the alkyl halide and the nucleophile | SN2 |
| An ___ reaction exhibits first-order kinetics | SN1 |
| An ___ reaction is unimolecular | SN1 |
| An ___ reaction's rate-determining step depends only on the alkyl halide's concentration | SN1 |
| All ___ reactions proceed with backside attack of the nucleophile, resulting in inversion of configuration at a stereogenic center | SN2 |
| Inversion of configuration in an ___ reaction is often called Walden inversion | SN2 |
| ___ reactions proceed with racemization at a single stereogenic center | SN1 |
| memorize |
SN2 Reactions
| Statement | Missing Words |
|---|
| As the number of R groups on the carbon with the leaving group increases, the rate of an SN2 reaction ___ | decreases |
| ___ undergo SN2 reactions with ease | methyl and 1o alkyl halides |
| ___ react more slowly | 2o alkyl halides |
| ___ do not undergo SN2 reactions | 3o alkyl halides |
| Increasing the number of R groups on the carbon with the leaving group ___ crowding in the transition state, decreasing the rate of an SN2 reaction | increases |
| The SN2 reaction is fastest with ___ | unhindered halides |
| Cells use ___ instead of alkyl halides such as CH3I in nucleophilic substitution reactions | SAM (s-adenosylmethionine) |
| memorize |
SN1 Reactions
| Statement | Missing Words |
|---|
| The SN1 mechanism has ___ | two steps |
| ___ are formed as reactive intermediates | carbocations |
| The ___ is heterolysis of the C-X bond | first step |
| The ___ is nucleophilic attack (a Lewis acid-base reaction) | second step |
| The ___ is slow | first step |
| The ___ is fast | second step |
| The ___ is rate-determining | first step |
| The carbocation (with three groups around C) is ___ hybridized and trigonal planar | sp2 |
| The carbocation contains a vacant ___ orbital extending above and below the plane | p |
| ___ from both sides of a planar carbocation occurs in SN1 reactions | nucleophilic attack |
| ___ is the formation of equal amounts of two enantiomeric products from a single starting material | racemization |
| As the number of R groups on the carbon with the leaving group ___, the rate of an SN1 reaction increases | increases |
| From left-to-right, the rate for SN1 reactions of R3CX, R2CHX, RCH2X, and CH3X ___ | decreases |
| ___ undergo SN1 reactions rapidly | 3o alkyl halides |
| ___ react more slowly | 2o alkyl halides |
| ___ do not undergo SN1 reactions | methyl and 1o alkyl halides |
| memorize |
Carbocation Stability
| Statement | Missing Words |
|---|
| As the number of ___ on the positively charged carbon atom increases, the stability of the carbocation increases | R groups |
| Inductive effects are electronic effects that occur through ___ | σ bonds |
| Electron donor groups (Z) stabilize ___ | cations |
| Electron-withdrawing groups (W) stabilize ___ | anions |
| Alkyl groups are ___ that stabilize a positive charge | electron donor groups |
| Spreading out charge by the overlap of an empty p orbital with an adjacent σ bond is called ___ | hyperconjugation |
| memorize |
The Hammond Postulate
| Statement | Missing Words |
|---|
| The rate of an SN1 reaction increases as the number of R groups on the carbon with the leaving group ___ | increases |
| The stability of a carbocation decreases as the number of R groups on the positively charged carbon ___ | decreases |
| The rate of an SN1 reaction increases as the stability of the carbocation ___ | increases |
| In endothermic reactions, the transition state is closer in energy to the ___ | products |
| In exothermic reactions, the transition state is closer in energy to the ___ | reactants |
| Transition states in endothermic reactions resemble the ___ | products |
| Transition states in exothermic reactions resemble the ___ | reactants |
| In an ___ reaction, the more stable product forms faster | endothermic |
| In an ___ reaction, the more stable product may or may not form faster because Ea is similar for both products | exothermic |
| In the SN1 reaction, the rate-determining step is the formation of the carbocation, an ___ reaction | endothermic |
| If the stability of the carbocation decreases, the rate of its formation ___ | decreases |
| memorize |
Predicting SN1 Versus SN2
| Statement | Missing Words |
|---|
| Increasing alkyl substitution favors ___ | SN1 |
| Decreasing alkyl substitution favors ___ | SN2 |
| Methyl and 1o halides (CH3X and RCH2X) undergo ___ reactions only | SN2 |
| 3o alkyl halides (R3CX) undergo ___ reactions only | SN1 |
| 2o alkyl halides (R2CHX) undergo ___ reactions | both SN1 and SN2 |
| Strong nucleophiles present in high concentration favor ___ reactions | SN2 |
| Weak nucleophiles favor ___ reactions | SN1 |
| Weak nucleophiles decrease the rate of any competing ___ reaction | SN2 |
| RO- and -OH are ___ nucleophiles | strong |
| ROH and H2O are ___ nucleophiles | weak |
| ___ nucleophiles usually have a net negative charge | strong |
| ___ nucleophiles are usually neutral | weak |
| A better leaving group increases the rate of ___ reactions | both SN1 and SN2 |
| Polar protic solvents are especially good for ___ reactions | SN1 |
| Polar aprotic solvents are especially good for ___ reactions | SN2 |
| Polar protic solvents favor ___ reactions because the ionic intermediates are stabilized by solvation | SN1 |
| Polar aprotic solvents favor ___ reactions because nucleophiles are not well solvated, and therefore are more nucleophilic | SN2 |
| The solvents H2O and CH3OH favor ___ reactions | SN1 |
| The solvents acetone [(CH3)2C=O] and DMSO [(CH3)2S=O] favor ___ reactions | SN2 |
| ___ reactions occur only at sp3 hybridized carbon atoms | both SN1 and SN2 |
| Vinyl halides and aryl halides both have a halogen atom bonded to an sp2 hybridized C and so do not undergo nucleophilic substitution by ___ reactions | both SN1 and SN2 |
| memorize |
Molecules Synthesized from R-X by SN2 Nucleophilic Substitution
| Nucleophile (:Nu-) | Product | Name |
|---|
| -OH | R-OH | alcohol |
| -OR' | R-OR' | ether |
| -O-(C=O)-R' | R-O-(C=O)-R' | ester |
| -CN | R-CN | nitrile |
| -:C≡C-H | R-C≡C-H | alkyne |
| N3- | R-N3 | azide |
| :NH3 | R-NH2 | amine |
| -SH | R-SH | thiol |
| -SR' | R-SR' | sulfide |
| | memorize |
Reference: Chapter 7 of Janice Gorzynski Smith's "Organic Chemistry" 2nd Edition,
McGraw-Hill, 2008 (ISBN=978-0-07-304986-1).
|
|
