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CHM231 Ch.7

QuestionAnswer
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
Created by: 817229501