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CHM231 Ch.7
| Question | Answer |
|---|---|
| What's a haloalkane? | Aka alkyl halide; It's a compound that contains a halogen covalently bonded to an sp3-hybridized carbon |
| What does “RX” represent? | A haloalkane |
| What's another name for a haloalkane? | Alkyl halide |
| In a haloalkane, which has the negative and the positive charge between the halogen and the carbon? | Halogen is negatively-charged and the Carbon is positively-charged |
| What's a methylhaloalkane? | The halogen's carbon isn't bonded to anymore carbons |
| What's a primary haloalkane? | The halogen's carbon is bonded to 1 other carbon |
| What's a secondary haloalkane? | The halogen's carbon is bonded to 2 other carbons |
| What's a tertiary haloalkane? | The halogen's carbon is bonded to 3 other carbons |
| Are haloalkanes polar or nonpolar? Why? | They're polar; Their halogen is more electronegative than the carbon they're bonded to |
| Are dipole-diple interactions or London dispersion forces (Van der Waals interactions) larger? | Dipole-dipole interactions |
| How do you name a haloalkane? | Number the longest parent chain, with the substituent encountered first the lowest number |
| What are two names for CH2Cl2? | Dichloromethane, Methylene chloride |
| What are two names for CHCL3? | Trichloromethane, Chloroform |
| What are two names for CH3CCl3? | 1,1,1-Trichloroethane, Methyl chloroform |
| What are two names for CH2=CHCl? | Trichloroethylene, Trichlor |
| What's the full name of “CFC”? | Chlorofluorocarbon |
| What's the significance of CFCs? | They're chemically inert, don't decompose in the lower atmosphere, & rise to the stratosphere and delete the ozone layer |
| What are two of the most widely used CFCs? | Freon-11 (CCl3F, Trichlorofluoromethane) & Freon-12 (Ccl2F2, Dichlorodifluoromethane) |
| What two reactions can haloalkanes undergo? | Nucleophilic substitution reactions and beta-elimination reactions |
| What happens during a nucleophilic substitution reaction? | A nucleophile attaches to the carbon and takes the place of the leaving group (the halogen) |
| Why do nucleophiles react with haloalkanes but not with alkanes? | Haloalkanes are polar and alkanes aren't |
| What class of compound is formed if it contains an -OH? | Alcohol |
| What class of compound is formed if it contains a -OR | Ether |
| What class of compound is formed if it contains a -SH | Thiol (mercaptan) |
| What class of compound is formed if it contains a -SR | Sulfide (thioether) |
| What class of compound is formed if it contains an -I | Alkyl iodide |
| What class of compound is formed if it contains an -NH3 | Alkylammonium ion |
| What are the two mechanisms of nucleophilic substitutions, and what makes up the difference between them? | Sn1 & Sn2 reactions; The difference is between the timing of the bond-breaking and bond-forming steps |
| How many species are involved in the rate-determining step of an Sn2 reaction? | 2 |
| What's the equation for the reaction rate of an Sn2 reaction? | Reaction rate = k*[haloalkane]*[nucleophile] |
| The rate of reaction of an Sn2 reaction depends on the concentration of what? | The haloalkane and the nucleophile |
| What happens in an Sn2 reaction? | The nucleophile attacks the Carbon on the side opposite the leaving group (halogen) and replaces it; Bond-breaking and bond-forming are simultaneous |
| What's a Walden inversion? | In an Sn2 reaction, when the nucleophile replaces the leaving group of a stereocenter, the other molecules configurations are inverted |
| What's the difference between -cis and -trans? | Cis = same side, trans = opposite side |
| In an energy diagram for an Sn2 reaction, there are _ transition states and _ reactive intermediates. | 1, 0 |
| Why is the reaction kinetic of an Sn2 reaction bimolecular? | Both the nucleophile and the leaving group are part of the slowest step in the reaction |
| What happens in an Sn1 reaction? | The leaving group breaks off from the carbon entirely before bonding with the nucleophile begins |
| How many species are involved in the rate-determining step of an Sn1 reaction? | 1 |
| What's the equation for the reaction rate of an Sn1 reaction? | Reaction rate = k*[haloalkane] |
| The rate of reaction of an Sn1 reaction depends on the concentration of what? | The haloalkane |
| What are the 3 steps of an Sn1 reaction? | 1) Leaving group breaks off & leaves a carbocation intermediate, 2) carbocation reacts with nucleophile, 3) proton transfer completes the reaction |
| What's the slowest, rate-determining step of an Sn1 reaction? | When the leaving group (haloalkane) breaks off of the carbon, giving a carbocation intermediate |
| What's nucleophilicity? | The rate at which a nucleophile attacks a reference compound under a standard set of experimental conditions |
| As the reaction rate increases, the nucleophilicity of the nucleophile _ | increases |
| What are good nucleophiles? | Anions |
| In which nucleophilic substitution mechanism do nucleophiles participate in the rate-determining step? | Sn2 |
| Which nucleophilic substitution pathway is independent of the of the nucleophile's nucleophilicity? | Sn1 |
| Do stronger nucleophiles favor Sn1 or Sn2 reactions? | Sn2 reactions |
| Define “electronic factors.” | They're the relative stabilities of carbocation intermediates |
| Are Sn1 or Sn2 reactions governed by electronic factors? | Sn2 |
| The higher the stability of the carbocation intermediate, the more likely the reaction will proceed according to the Sn1 or Sn2 reaction? | Sn1 |
| Arrange the stabilities of these carbocations: methyl, primary, secondary, tertiary | tertiary > secondary > primary > methyl |
| Define “steric factor.” | It is the relative ease the nucleophile has of approaching the site of reaction |
| Arrange the relative rates of steric factors: methyl, primary, secondary, tertiary. | Methyl > primary > secondary > tertiary |
| What's the leaving group? | The part of the molecule that's substituted by the nucleophile |
| What usually act as good leaving groups? | Conjugate (weak) bases of strong acids |
| Arrage the relative acidities of these hydrogen halides: HF, HCl, HBr, HI. | HI > HBr > HCl > HF |
| Arrange the leaving abilities of these halide anions: I-, Br-, Cl-, F- | I- > Br- > Cl- > F- |
| Are conjugate bases of weak or strong acids poor leaving groups? | Weak acids |
| Name three strong base parts | OH-, RO-, NH2- |
| Does an acid or base ion have a greater ability as a leaving group? | Acid ion |
| What's a protic solvent and what do they do? | A solvent that contains an -OH or -NH group; They stabilize the carbocations through solvation |
| Do protic solvents favor Sn1 or Sn2 reactions? | Sn1 |
| What's an aprotic solvent? | A solvent that does not contain an -OH or -NH group |
| Do aprotic solvents favor Sn1 or Sn2 reactions? | Sn2 |
| What happens to a methylhaloalkane (CH3X) in an Sn1 & Sn2 reaction? | The Sn2 reaction is favored and the Sn1 doesn't occur; It's because the methyl cation is so unstable that it's never observed in solution |
| What happens to a primary haloalkane (RCH2X) in an Sn1 & Sn2 reaction? | The Sn2 reaction is favored & the Sn1 doesn't occur; It's because primary carbocations are so unstable that they're never observed in solution |
| What happens to a secondary haloalkane (R2CHX) in an Sn1 & Sn2 reaction? | Sn2 is favored in aprotic solvents with good nucleophiles, & Sn1 is favored in protic solvents with poor nucleophiles |
| What happens to a tertiary haloalkane (R3CX) in an Sn1 & Sn2 reaction? | Sn2 doesn't occur, & Sn1 is favored |
| What happens when a haloalkane is substituted at a stereocenter in an Sn1 reaction? | Inversion of configuration |
| What happens when a haloalkane is substituted at a stereocenter in an Sn2 reaction? | Racemization |
| What's “inversion of configuration” in an Sn2 reaction? | When the nucleophile attacks the stereocenter from the side opposite the leaving group |
| What's “racemization” in an Sn1 reaction? | When the carbocation intermediate is planar, and the attack by the nucleophile occurs with equal probability from either side |
| What are the three components of a nucleotide? | Phosphate group, sugar, & nitrogenous base |
| How do alkylating anti-cancer agents work? | Their nucleophilic substitutions crosslink DNA strands of the cell, thereby preventing cell division |
| What haloalkane reaction does methylbromide do and what does it act as a fumigant against? | Nucleophilic substitution; It's a fumigant against insects, termites, rodents, weeds, nematodes, & soil-borne diseases |
| What's a beta elimination? | The removal of atoms or groups of atoms from adjacent carbons to form a carbon-carbon double bond |
| What's dehydrohalogenation? | The elimination of HX, with X = Cl, Br, or I |
| What's the Zaitsev rule? | If several beta-hydrogen atoms are available for elimination, the major product is the more stable (more highly substituted) alkene |
| What are the two limiting mechanisms for beta-elimination reactions? | E1 & E2 |
| What type of bases are used in beta-elimination reactions, and give examples | Strong bases, like OH-, OR-, & NH2- |
| What's an E2 mechanism? | A one-step mechanism in which the breaking of the C-X & C-H bonds is concerted (simultaneous) |
| What does “concerted” mean? | Simultaneous |
| The reaction rate of an E2 reaction depends on the concentration of what? | the haloalkane and the base |
| What's the equation for reaction rate of an E2 mechanism? | rate = k * [haloakane]* [base] |
| What's an E1 mechanism? | When the breaking of the C-X bond is complete before the reaction with the base breaks the C-H bond |
| The reaction rate of an E1 mechanism depends on the concentration of the what? | the haloalkane |
| What's the equation for the reaction rate of an E1 mechanism? | rate = k * [haloakane] |
| The E2 mechanism of a beta-elimination reaction is similar to what mechanism of the nucleophilic substitution? | Sn2 |
| The E1 mechanism of a beta-elimination reaction is similar to what mechanism of the nucleophilic substitution? | Sn1 |
| What are the steps of an E1 mechanism? | 1) Ionization of a C-X gives a carbocation intermediate, 2) Proton transfer from the carbocation intermediate to a base gives an alkene |
| The greater the nucleophilicity of the attacking molecule | ion, the [greater or smaller?] the _:_ ratio |
| The greater the basicity of the attacking molecule | ion, the greater the [greater or smaller?] the _:_ ratio |
| What reactions for methylhaloalkanes are observed? | Sn2 |
| What reactions for primary haloalkanes are observed? | Sn2 & E2 |
| What reactions for secondary haloalkanes are observed? | Sn2, E2, & Sn1 |
| What reactions for tertiary haloalkanes are observed? | E2, Sn1 |
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