Elimination Reactions

krabi's version from 2015-06-11 01:59

Section 1

Question Answer
What is the trend for CC Stability? 3 > 2 > 1 > methyl just like radicals.
What happens during the 3rd final step of E1? A water molecule deprotonates the CC ⇒ forms an alkene.
What is the major product in E1?Major product is always the most substituted alkene w/most friends.
What is the Saytzeff Rule? The major product of elimination will the most substituted alkene.
When does dehydrohalgenation -- goes through E1 mechanism rx? IF there is absence of strong base; THEN E1.
When does dehydrohalgenation -- goes through E2 mechanism rx? IF there is ++ concentration of strong, bulky base THEN E2
Compare E1 with E2 rx.In E1, halogen drops off & H is removed in 2nd step; whereas, in E2 the base removes the H from carbon parked next door to the halogen-containing carbon, halogen drops off and leaves an alkene.

Section 2

Question Answer
Compare steps in Sn1 and Sn2 rx. The E1 is in one step because the bulky base prevents Sn2 If the base is too bulky, Saytzeff is violated, leaving the LEAST substituted alkenes.
Compare elimination & substitution.In elimination the base abstracts an H; by contrast, in substitution rx the Nuc- attacks the carbon
Give an example of an Addition RxHydrogenation is an addition rx.
What is needed for hydrogenation? A hetereo catalyst is needed (exists in a different phase than the reactants/products)
What is Syn Addition?Is Same side addition;Paradox - Always creates a cis-alkene.
What is the Energy of hydrogenation? It is exothermic with a ++ High Energy of activation.
Define Hydrogenation:Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, generally an alkene.
State hydrogenation trends The lower heat of hydrogenation ⇒ the more stable alkene.

Section 3

Question Answer
How does Oxidation impact alkenes?Creates glycols or OH groups on the adjacent carbon; or, 2) oxidation may cleave the alkene at the double bond (ozonolysis).
What is ozonolysis?Breaking an alkene bond using Ozone; also, alkynes produce COOH during ozonelysis
What is an electrophile? An electron loving species w/partial positive charge (even if from momentary dipole)
Give an examples of Electro (+)double bond of an alkene

Section 4

Question Answer
Define Markovnikov’s rule? The Hydrogen will be added ⇒ to the least substituted dbond. H goes for the single DB.
When do hydrogen halides (HI, HF) follow Markovnikov’s rule? When Hydrogen halides are added to alkenes
What are Hydrogen Halides?hydrogen halides (HI, HF)
What is the 1st step of Electrophilic Addn w/halides? First, the hydrogen halide (a BL acid) creates a charged +ve proton. This acts as an Electro (-).
What is the 2nd step of Electrophilic Addn with halides?The newly formed CC picks up the negative charged halide ion
Rate determining steps of Electrophilic Addn?The first step is the slow step and therefore determines the rate.
What is the peroxide exception? Called what? If ROOR perioxides are present, then bromine (not H) will add to the least substituted carbon in Electrophillic addn. Is the Anti-Markovnikov.