Test 2 Flashcards
(Ch 6)
a. Define: Alkyl halide
b. Vinyl halide
c. Aryl halide
a. Halogen directly bonded to sp3 carbon
b.halogen bonded to sp2 carbon of alkene
c.halogen bonded to sp2 carbon on benzyne ring
(Ch 6)
a. what group are halogens in?
b. describe a c-halogen bond
c. what happens to C and Halogen when they react?
a.7A
b. polar; Halogens more electronegative than C, C has partial + charge
c. C can be attacked by nucleophile(New C-nuc bond formed) and halogen can leave with e pair(existing C-X bond broken)
(Ch 6) Alkyl Halide classification:
a. Methyl Halide
b. Primary Halide
c. Secondary Halide
d. Tertiary Halide
a. Halide attaches to methyl group
(CH3-X)
b. C bonded to halide attaches to one other carbon
(R-CH3-X)
c. C bonded to halide attaches to two other carbons.
( R )
(R-CH3-X)
d. C bonded to halide attaches to three other carbons
( R )
(R-CH3-X)
( R )
(Ch 6)
a. IUPAC Nomenclature
b. Reaction of Alkyl Halides:
-nucleophilic substitution:
-elimination:
a. name as haloalkane, choose longest c chain, use lowest # for position
b.
-C-Nu bond formed and C-X bond broken
-Major product formed + halogen
(Ch 6)
a.Sn2 Mechanism:
b. What type of reaction?
c. what does concerted mean?
a. Bimolecular nucleophilic substitution
b. One-step concerted reaction
c. Bond breaking and making occur in the same step “in concert”
(Ch 6) Sn2 cont:
a. Substitution: Reactants and products?
b. define
c. Rxn rate and overall order?
a. nucleophile + substrate(electrophile) –> transition state (substrate connected to nuc) –> Nuc-substrate + halogen (leaving group)
b. Halogen atom on alkyl halide replaced(substituted) w/ nucleophile(HO-)
c. Kr[alkyl halide][nucleophile], 2nd
(Ch 6) Sn2 cont:
a. draw and label energy diagram
b. Mechanistic considerations (Walden Inversion):
c. Under what circumstances will this process not occur?
a. reactants, transition state (highest energy), products (lowest energy).
b.because it is concerted, Sn2 substitution occurs with the inversion of stereochemistry at the electrophilic center. (like wind inverting umbrella, turns (S) to (R) and vice versa.
c. If the process breaks Cahn Ingold Prelogs by changing the priorities.
(Ch 6) Sn2 cont:
a.Substrate Structure (steric effects and where nuc attacks):
b.Relative rxn rates for sn2 order:
a. Nucleophile “attacks” from back side of atom: must overlap back lobe of C-X sp3 orbital.
b. CH3X>1>2>3(3 doesn’t react due to steric hindrance aka too crowded)
c.
(Ch 6)
a.Nucleophilic strength:
b.Trends in Nucleophilicity
c. Polarizability effect of Nucleophilic strength:
a. Nucleophiles react faster; strong bases are nucleophiles, but not all strong nucleophiles are basic.
b. -negatively charged nucleophile stronger than its neutral counterpart
-nucleophilicity decreases from left to right on periodic table
-increases down periodic table as size and polarizability increase
c. Bigger atoms have “softer/squishier” shell that can start to overlap the carbon atom from further distance.
(Ch 6)
a.Sn1 mechanism:
b. Rate:
c. What is created and what occurs?
d. Define racemization?
a. Unimolecular nucleophilic substitution (only halogen involved in rate determining step)
b. kr[alkyl halide]
c. carbocation intermediate; Nucleophilic attack occurs, giving a mix of inversion and retention, leading to racemization
d. equal mixture of enantiomers. Carbon rehybridizes sp3 C (chiral, optically active) and becomes sp2 C (achiral, optically inactive).
(Ch 6) Sn1 cont.
a. Sn1 steps:
1.Formation of carbocation (what occurs and what is involved)
2.Attack of the nucleophile
3.possible proton inventory
- rate-determining step, only substrate involved. RACEMIZATION OCCURS HERE: all stereochemical info at electrophile carbon is lost.
- Nucleophile attacks carbocation forming product, nucleophile can be very weak bc C+ is a strong electrophile.
- If nucleophile is neutral, this step is necessary; If uncharged molecule (alcohol/h2o), the positively charged product must lose proton.
(Ch 6) Sn1 cont.
a. Define energy diagram
b.Stereochemical consequences
-structure:
-nucleophilic attack:
c. what is produced after nucleophilic attack?
d. substituent effects (carbocation stability):
a. peak 1 transition state 1, slowest step is rate-determining step (valley), peak 2, low energy products
b. -carbocations sp2 hybridized and trigonal planar
-nucleophilic attack occurs on empty p orbitals, so in Sn1, can occur on top or bottom lobes.
c. mixtures of retention and inversion of configuration at the electrophilic center (if chiral, gets racemized).
d. inductive effect and hypercojugation
(Ch 6) Sn1 cont.
a.order of reactivity:
b. Better leaving group:
c.Inversion and what happens:
1.hydride shift
2.methyl shift
3.why does this occur?
d. retention
a. 3>2> (follows carbocation stability)
b. Increases rate of rxn
c. carbocations can rearrange to form more stable carbocation; move the smallest group on adjacent carbon (creates hydride and methyl shift)
1. H- on adjacent carbon moves
2. CH3- on adjacent carbon moves
3. poor nucleophile in sn1 causes it.
d. “retains” bond w/ nucleophile.
(Ch 6)
a. Why are the best leaving groups stable after they leave?
b. which Sn has rearrangements?
a.e withdrawing to polarize c atom, stable(not strong base) after leaving, and polarizable to stabilize transition state.
b. Sn1
(Ch 6) Solvent effects Sn2:
a.define its protic state:
b. define its aprotic state:
*(which one does it use?)
c. Sn2 crown ethers
a. Solvates nucleophiles, reducing nucleophilicity because of acidic hydrogens (O-H, N-H). BAD for Sn2 nucleophiles (ex, alcohols C6H10).
b. Do not H-bond b/c they dont have acidic protons, so doesnt solvate and allows nucleophile to be more free. SUITABLE for sn2
*uses aprotic solvent
c. All C and O’s are sp3, so structure looks like crown. solvate cation so nucleophilic strength of anion increases.
