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