Organic 4: Alcohols & Alkyl Halides Flashcards
Functional group
atom or group in a molecule most responsible for the reaction the compound undergoes under a prescribed set of conditions
Mechanism
how the structure of the reactant is transformed to that of the product
Alcohols
compound of the type R-OH
Alkyl halides
compound of the type RX, in which X is a halogen substituent (F, Cl, Br, I)
R
stands for an alkyl group
Functional class nomenclature
alkyl group & halide are designated as separate words; alkyl group named on the basis of its longest continuous chain beginning at the carbon to which the halogen is attached; alkyl + halide
Substitutive nomenclature
treats the halogen as a halo substituent on an alkane chain; carbon chain numbered in the direction that gives the substituted carbon the lower number; locants required
Induced-dipole/induced-dipole forces
the only intermolecular attractive forces available to nonpolar molecules such as alkanes and are important in polar molecules as well
Dipole-dipole attractive force
2 molecules of a polar substance experience a mutual attraction between the positively polarized region of one molecule and the negatively polarized region of the other
Dipole/induced-dipole force
combines features of both the induced-dipole/induced-dipole & dipole-dipole attractive forces; a polar region of 1 molecule alters the electron distribution in a nonpolar region of another in a direction that produces an attractive force between them
Hydrogen bonding
type of dipole-dipole attractive force in which a positively polarized hydrogen of 1 molecule is weakly bonded to a negatively polarized atom of an adjacent molecule; typically involves the hydrogen of one -OH or -NH group and the oxygen or nitrogen of another
Polarizability
induced-dipole/induced-dipole attractions are favored when the electron cloud around an atom is easily distorted; more pronounced when the electrons are farther from the nucleus than when they are closer
Substitution
reaction of an alcohol with a hydrogen halide; a halogen, usually Cl or Br, replaces a hydroxyl group as a substituent on carbon
Mechanism
step-by-step pathway of bond cleavage and bond formation that leads from reactants to products
Elementary step
a step in a reaction that involves only one transition state
Concerted reaction
reaction that occurs in a single elementary step
Alkyloxonium ion (ROH2+)
proton transfer to an alcohol results in this
Molecularity
the number of species that react together in the same elementary step of a reaction mechanism
Bimolecular
a process by which 2 particles react in the same elementary step
Intermediate
transient species formed during a chemical reaction; typically, it is not stable under the conditions of its formation and proceeds further to form the product; unlike a transition state, which corresponds to a maximum along a potential energy surface, this lies at a potential energy minimum
Potential energy diagram
plot of potential energy versus some arbitrary measure of the degree to which a reaction has proceeded (the reaction coordinate); the point of maximum potential energy is the transition state
Transition state
point of maximum potential energy encountered by the reactants as they proceed to products
Hammond’s Postulate
if 2 states are similar in energy, they are similar in structure
Carbocation
an ion that contains a positively charged carbon
Unimolecular
describing a step in a reaction mechanism in which only 1 particle undergoes a chemical change at the transition state
Electrophilic
electron-loving or electron-seeking; Lewis acids (electron-pair acceptors)
Nucleophiles
Lewis bases that react with electrophiles; “nucleus seekers”; have an unshared electron pair they can use in covalent bond formation
Rate-determining step
slowest step in a reaction; a reaction can proceed no faster than its slowest step
SN1 Mechanism
Substitutive nucleophilic unimolecular mechanism; mechanism for nucleophilic substitution characterized by a 2-step process; the 1st step is rate-determining and is the ionization of an alkyl halide to a carbocation and a halide ion
Hyperconjugation
delocalization of electrons in a sigma bond through a system of overlapping orbitals
SN2 Mechanism
nucleophilic substitutions that have a bimolecular rate-determining step
Kinetics
study of the rates of chemical reactions and the factors that influence reaction rate
Halogenation
replacement of a hydrogen by a halogen; the most frequently encountered examples are the free-radical ________ of alkanes and the ________ of arenes by electrophilic aromatic substitution
Free Radicals
species that contain unpaired electrons
Spin density
measure of unpaired electron density at a particular point in a molecule (tells us where the unpaired electron is most likely to be)
Homolytic cleavage
bond between 2 atoms is broken so that each of them retains one of the electrons in the bond
Heterolytic cleavage
bond between 2 atoms is broken, but one fragment retains both electrons
Bond dissociation enthalpy (D)
energy required for homolytic bond cleavage
Endothermic
a positive value for heats of reaction signifies this type of reaction, where the reactants are more stable than the products
Initiation step
a process which causes a reaction, usually a free-radical reaction, to begin but which by itself is not the principal source of products; the ___ ___ in the halogenation of an alkane is the dissociation of a halogen molecule to 2 halogen atoms
Propagation steps
elementary steps that repeat over and over again in a chain reaction; almost all of the products in a chain reaction arise from these
Chain reaction
reaction mechanism in which a sequence of individual steps repeats itself many times, usually because a reactive intermediate consumed in 1 step is regenerated in a subsequent step; the halogenation of alkanes is a chain reaction proceeding via free-radical intermediates
Chain-terminating steps
a chemical reaction that stops further growth of a polymer chain
Photochemical reactions
reactions that occur when light energy is absorbed by a molecule
