Chapter 6 Flashcards
the most characteristic reaction of alkenes is … to the C-C double bond in such a way that the pi bond is …, and, in its place, … bonds form to two new atoms or groups of atoms
addition; broken; sigma bonds form;
another addition reaction of alkenes is a formation of … in the presence of certain catalysts called …, many alkenes form polymers made by the addition of … to a growing …
chain-growth polymers; initiators; monomers; polymer chain
in a reaction that occurs in two or more steps, each step has its own … and …
transition state; activation energy
a reactive intermediate corresponds to an … between two transition states
reactive intermediate
because the energies of the intermediates are higher than that of either reactants or products, they are highly … and usually cannot be …
reactive; isolated
the slowest step in a multistep reaction, called the …, is the step that crosses the …
rate-determining step; highest energy barrier
each step of a chemical reaction involves the crossing of a peak on an energy diagram. the peaks represent chemical structures on the energy ssurfaces that are … between …
transitions; stable structures
reaction intermediates are represented in wells (troughs) on the energy surfaces. the peaks on the surface are referred to as
transition states
reaction intermediates have lifetimes … than the time it takes for a bond to vibrate, whereas transition states have lifetimes only on the order of the … of a bond vibration. The chemical structures of transition states can be considered as having no …
longer; lifetime; measurable lifetime
equilibrium in a chemical reaction usually favors the side with stronger
chemical bonds
bond strengths are reported as …, defined as the energy needed to … any bond
bond dissociation enthalpies; break
the overall reaction of electrophilic species adding to pi bonds is called .. The key step in these mechanisms involves the pi electrons of the alkene reacting as a … or … with an … species
electrophillic addition; nucleophile; Bronsted-Lowry base; electrophilic
three features can make a molecule or an ion electrophilic:
- a region of low …, reflected by a … or .. charge. This aids reaction with an electron rich region of a nucleophile through …
- the lack of an … on an atom
- a relatively … to an atom that can depart as a … or … These can be considered electron-seeking because their reactions with nucleophiles create … and therefore more … molecules
electron density; partial; full positive; electrostatic attraction; octet; weak bond; stable ion; molecule; stronger bonds; stable
the hydrogen halides HCl, HBr, and HI add to alkenes to give … These additions may be carried out either with the pure reagents or in the presence of a … such as acetic acid
haloalkenes; polar solvent
a regioselective reaction is a reaction in which one direction of … or … occurs in preference to all others
bond forming; breaking
Regioselectivity was noted by Vladimir Markovnikov who made the generalization known as Markovnikov’s rule: in the addition of H–X to an alkene, hydrogen adds to the double-bonded carbon that has the …
greater number of hydrogens already bonded to it
electrophilic addition steps:
- add a ..
- make a new bond between a … and an …
proton; nucleophile; electrophile
the pi bond is relatively electron-rich because the pi bonding electron density is … and … the bond axis, not between the positively charged atomic nuclei as is the case with sigma bonding e- density –> more …
above; below; delocalization
Step 1 in proton addition rxns (the addition of a proton to the alkene) results in formation of a … called a …
cationic intermediate; carbocation
all carbocations are … as well as …
electrophiles; Lewis acids
the carbocation has an
empty p orbital
the physical structure of the transition state is the … that gives way to the carbocation intermediate
lowest-energy contorted geometry
the second step of the proton addition rxn is much easier than the first because the reactant is now a …, which is a highly reactive electrophile due to their … and the lack of an … at C
carbocation; positive charge; octet
because the highly electrophilic cation intermediate is so unstable, the energy necessary in the collision to surmount the second barrier is
very low
Reaction of HX and an alkene can, at least in principle, give two different carbocation intermediates because the proton could be transferred to either of the doubly bonded C atoms. We know, though, that a … carbocation is more stable and requires a lower Ea for its formation than a …, and a … carbocation is more stable and requires a lower Ea for its formation than a … carbocation. A more stable carbocation intermediate forms … than a less stable carbocation intermediate
tertiary; secondary; secondary; primary; faster
Alkyl groups stablize carbocations through …, which involves partial … of the sigma bonding orbital of an adjacent C-H or C-C bond of the alkyl group with the … of the cationic C. In other words, some e- density of the alkyl group C-H or C-C bond is mixed into the ..
hyperconjugation; overlapping; vacant 2p orbital; 2p orbital
the net result of hyperconjugation is an increase of … on the cationic carbon, thereby … the positive charge onto the adjacent alkyl groups. As more alkyl groups are bonded to a cationic carbon, the hyperconjugation effect becomes … and the carbocation becomes more …
electron density; delocalizing; stronger; stable
in the presence of an acid catalyst, most commonly concentrated sulfuric acid, water adds to an alkene to give an … The addition of water is called ..
alcohol; hydration
in the case of simple alkenes, H adds to the carbon of the double bond according to … and OH adds to the carbon with the …
Markovnikov’s rule; fewer hydrogens
mechanism for acid-catalyzed hydration:
- add a … (water reacts with H2SO4 to form …)
- make a new bond between a … and an …
- take a … away: it is lost to the … in solution, and the product yields a new …
proton; hydronium ion; nucleophile; electrophile; proton; water; acid catalyst (H3O+)
rearrangement: sometimes, if it creates a more stable structure, either an … or a … migrates, each with its bonding electrons, from an adjacent atom to the … atom
alkyl group; hydrogen; electron-deficient atom
carbocation rearrangement mechanism
- Add a …
- …
- make a new bond between a … and an …
proton; 1, 2 shift; nucleophile; electrophile
Cl2 and Br2 react with alkenes at room temp by adding halogen atoms to the two Cs of the double bond. F2 adds to alkenes but because its reactions are very … and …, this reaction is not useful. I2 also adds, but is also …
fast; difficult to control; not useful
the addition of Br or Cl to a cycloalkene is an example of a … reaction, in which one … is formed in preferred to all others
stereoselective; stereoisomer
Cl2 and Br2 as reagents add … –> they occur with ..
anti; anti stereoselectivity
Mechanism for addition of Br2/Cl2 with anti stereoselectivity:
- make a new bond between a … and an .. –> rxn is initiated by interaction of the … with … A … or … is formed
- make a new bond between a … and an … –> attack of … on … from the side … opens the ring to give the anti product
nucleophile; electrophile; pi electrons; bromine/chlorine; bridged bromonium ion or bridged chloronium ion; nucleophile; electrophile; bromide ion; C; opposite the bromonium ion
the bromines/chlorines are not only anti but also … Thus, this is an … attack
in the same plane (coplanar); anti-coplanar
Addition of Cl or Br to cyclohexene and its derivates gives a … product because only … positions on adjacent atoms of a cyclohexane ring are … and …
trans diaxial; axial; anti; coplanar
treating an alkene with Br2 or Cl2 in the presence of water results in addition of … and …, or … and …, to the C-C double bond to give a …
OH; Br; OH; Cl; halohydrin
Addition of HOCl and HOBr is … and …
regioselective; anti stereoselective
Mechanism for halohydrin formation and its anti stereoselectivity:
- make a new bond between a … and an …: reaction of the … with … gives a … intermediate
- make a new bond between a … and an …: attack of … ( a… ) on the … substituted C of the bridged ion opens the ring.
- take a … away
nucleophile; electrophile; pi electrons; bromine; bridged bromonium ion; nucleophile; electrophile; H2O; nucleophile; more; proton
(for halohydrins) The C-halogen bond to the more substituted carbon of the halonium ion is … than the bond to the less substituted carbon. this difference in lengths means that the ring-opening transition state can be reached more easily by attack at the … C
longer; more substituted
the result of oxymercuration followed by sodium borohydride reduction is … of … to an alkene
Markovnikov addition; H-OH
oxymercuration is …: HgOAC becomes bonded to the … of the alkene, and OH of water becomes bonded to the … C
regioselective; less substituted C; more substituted
Reduction of the organomercury compound by sodium borohydride (NaBH4) replaces HgOAc by …
H
oxymercuration reduction occurs without because no … is formed
rearrangement; free carbocation intermediate
mechanism for oxymercuration-reduction of an alkene:
- … to give stable molecules/ions: dissociation of mercury(II) acetate gives … (an …) and acetate anion
- make a new bond between a … and an …: attack of the … onto … forms a … intermediate (this is not a true …)
- make a new bond between a … and an …: anti attack of … on the bridged intermediate occurs at the … C to open the ring
- take a … away: transferred to …
- reduce the C-HgOAc bond to …
break a bond; AcOHg+; electrophile; nucleophile; electrophile; alkene pi bond; AcOHg+; bridged mercurinium ion; carbocation; nucleophile; electrophile; water; more substituted; proton; water; C-H
the net reaction from hydroboration and subsequent oxidation of an alkene is …
hydration of a C-C double bond
the regiochemistry of hydroboration and subsequent oxidation is …
non-Markovnikov
hydroboration-oxidation occurs without
rearrangement
hydroboration is the addition of … (..) to an alkene to form a …
borane; BH3; trialkylborane
Because of the vacant 2p orbital in the valence shell of boron, BH3, and all other trivalent compounds of boron are … They resemble …, but they are …
electrophiles; carbocations; electrically neutral
addition of borane to alkenes is … and …:
upon addition of borane to an unsymmetrical alkene, boron becomes bonded predominantly to the … C of the double bond (…)
H and B add from … of the double bond; that is, the reaction is … stereoselective
regioselective; stereoselective; less substituted; non-Markovnikov; the same face; syn
hydroboration mechanism:
- lewis acid-base …
- make a new bond between a … and … with simultaneous …: the boron adds to the … C, due to … and some … effects
coordination; nucleophile; electrophile; bond formation to H; less substituted; steric; electronic
… is an oxidizing agenet and oxidizes a trialkylborane to an alcohol and sodium borate
hydrogen peroxide
oxidation of a trialkylborane by alkaline hydrogen peroxide
- make a new bond between a nucleophile and an electrophile: donation of a pair of e- from a … to the … atom of the trialkylborane gives an intermediate in which boron has a … charge
- …: rearrangement of an R group to an … results in ejection of … ion (occurs twice)
- reaction of the trialkylborate with aqueous NaOH gives the …
hydroperoide ion (nucleo); boron (electrophile); negative formal; 1,2 shift; adjacent oxygen; hydroxide; alcohol
hydrogen peroxide oxidation of a trialkylborane is … in that the configuration of the alkyl group is retained. The net result of hydroboration-oxidation of an alkene is … stereoselective addition of … and … to a C-C double bond, combined with … regioselectivity
stereoselective; syn; H; OH; non-Markovnikov
oxidation is the … of electrons and reduction is the … of electrons
loss; gain
oxidation: the addition of … to and/or removal of … from a C atom
O; H;
reduction: the removal of … from and/or addition of .. to a C
O; H
oxidation of an alkene by OsO4 is … stereoselective
syn stereoselective
oxidation of an alkene by OsO4 involves syn addition of an … group to each C of the double bond
OH
the syn stereoselectivity of the osmium tetroxide oxidation of an alkene is accounted for by the formation of a cyclic osmate in such a way that the five-membered osmium-containing ring is bonded in a … configuration to the original alkene
cis
usually, the osmate is treated directly with a …, such as …, which cleaves the osmium-oxygen bonds to give a … and reduced forms of osmium
reducing agent; NaHSO3; cis glycol
ozonolysis cleaves the C-C double bond and forms two … groups in its place
carbonyl C=O
O3 is strongly
electrophilic
ozonolysis is one of the few organic reactions that breaks
C-C bonds
mechanism for ozonolysis:
- ozone reacts with the alkene with both … and … character in a single, simultaneous step
- break a bond to give stable molecules/ions: relocating valence e- in the molozonide results in … of one C-C and one O-O bond. the fragments then recombine to form an …
- reduction of the ozonide and … results in the final carbonyl fragments
electrophilic; nucleophilic character; cleavage; ozonide; cleavage
conversion of an alkene to an alkane involves reduction by … in the presence of a …: process is …, or …
hydrogen; catalyst; catalytic reduction; catalytic hydrogenation
catalytic reduction is …, with the vast majority proceeding by … addition of H to the C-C double bond
stereoselective; syn;
an optically active compound can never be produced from … starting materials reacting in an … environment
achiral; achiral
an enantiomerically pure product may be produced from … reagents if the reaction takes place in a … environment
achiral; chiral
a stereospecific rxn is a special type of stereoselective reaction in which the stereochemistry of the product depends on the …
stereochemistry of the starting material
in catalytic reductions where a new chiral center is formed, a large enantiomeric excess of one enantiomer may be formed, and the reaction is said to be
enantioselective
