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O Chem Exam 2
O chem set
59
Organic Chemistry
Undergraduate 3
10/17/2013

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Term
3 Reactions Alkanes Can Undergo
Definition
1)Combustion
2)Cracking and Hydrocracking
3)Halogenation
Term
Combustion
Definition
Rapid oxidation that takes place at high temperatures
converting alkanes to carbon dioxide and water
little control is possible except for control of temp
CnH(2n+2) + excess O2 >heat> nCO2 + (n+1)H2O
Term
Cracking and Hydrocracking
Definition
Large hydrocarbons at high temps produce smaller hydrocarbons
-catalyst
Term
Halogenation
Definition
heat or light usually needed to initiate
alkanes reacting with halogens to form alkyl halides
fluorine—to fast to control
Iodine—reacts slowly or not at all
Term
Chair conformation
Definition
-Most stable cyclohexane conformation
-all C-C bonds are 109.5 degrees
Term
Boat confirmation
Definition
-bonds angles of 109.5 degrees and avoids angle strain
-suffers from torsional strain because there is an eclipsing of bonds
-eclipsing causes flagpole hydrogens to interfere with one another
Term
Twist Boat confirmation
Definition
-more stable than boat
-flagpole hydrogens move away from each other so the eclipsing bonds are reduced
-twist boat is lower in energy than boat
Term
Half-chair confirmation
Definition
-highest energy and the most unstable
Term
chair-chair interconversion "ring flip"
Definition
-changes axial to equatorial and vice versa
-figure 3-23
Term
Axial bonds
Definition
directed up and down
Term
Equatorial bonds
Definition
point out from the ring—equatorial is more stable than axial
*equatorial bonds have lower energy so the more equatorial bonds are more stable
Term
Torsional strain
Definition
strain you get when things are eclipsed
—resistance to twisting
Term
Angle strain
Definition
when C-C bonds do not have angles of 109.5
Term
Ring strain
Definition
Torsional + Angle strain
Term
Steric strain
Definition
groups so close that their electron clouds experience a strong repulsion
Term
Fused rings
Definition
-most common
-chare two adjacent carbon atoms and the bond between them
bicyclo[#.#.#]...
Term
Bridged rings
Definition
-share one or more nonadjacent carbon atoms
bicylo[#.#.#]...
Term
Spirocyclic compounds
Definition
two rings share only one carbon atom, relatively rare
spiro[#.#.#]...
Term
Enantiomers
Definition
Non-superimposable mirror-image molecules; mirror-image isomers
Term
isomers
Definition
different compounds with the same molecular formula
Term
diastereomers
Definition
steroisomers that are not mirror images
Term
racemic mixture
Definition
a mixture of equal quantities of enantiomers
Term
Intiation step
Definition
generates a reactive intermediate
—always require light or heat to trigger
Term
Propogation steps
Definition
reactive intermediates react with a stable molecule to form a product and another reactive intermediate
**one RI and radical on each side of equation
Term
Termination step
Definition
side reactions that destroy reactive intermediates and tend to slow or stop the reaction
**getting rid of radicals
Term
Reactive intermediate
Definition
a short-lived species that is never present in high concentration because it reacts as quickly as it is formed
Term
radicals
Definition
species with unpaired electron
Term
homolytic
Definition
a bond breaks so that each bonded atom gets an electron
Term
heterolytic
Definition
one of the atoms retains both electrons
Term
Carbocation
Definition
species that contains a carbon atom with a positive charge
Term
Carbonanion
Definition
species that contains a a pair of nonbonding electron and are negatively charged
Term
Carbene
Definition
divalent that has two nonbonding electrons on the divalent carbon atom
Term
rate-limiting step
Definition
slowest step in a multistep sequence of reactions
Term
enthalpy
Definition
a measure of the heat energy in a system
Term
endothermic
Definition
consuming energy (positive H)
Term
exothermic
Definition
giving off heat (Negtive H)
Term
catalyst
Definition
a substance that increases the rate of a reaction (By lowering Ea) without being consumed in the reaction
Term
Hammond Postulate
Definition
Related species (on a reaction-energy diagram) that are closer in edgy are also closer in structure. In an exothermic reaction, the transition state is closer to the reactants in energy and in structure. In an endothermic reaction, the transition state is closer to the products in energy and in structure.
Term
Chiral center
Definition
4 different connected atoms
Term
allene
Definition
compound have two C=C DB that meet at a single carbon ; many allenes are chiral
Term
Chiral
Definition
"handed"
Term
Superimposable
Definition
they can be placed atop one another and the three-dimensional position of each atom of one molecule coincides with the equivalent atom of the other molecule
Term
Internal Mirror Place
Definition
cut in half and is the same on both sides—a chiral
**any molecule that has a n internal mirror place of symmetry cannoth be chiral, even though it may contain asymmetric carbon atoms
Term
Cahn-Ingold-Prelog convention
Definition
(R&S system) naming the configurations of chirality centers
1. assign priority
R=clockwise
S=Counterclockwise
Term
polarimetry
Definition
measure of the plane rotation
*can only have with chiral compounds
*only chiral compounds are optically active
Term
meso compound
Definition
achiral compounds with chiral centers
Term
Ways to resolve diastereomers
Definition
distillation, recrystallazation, chromatography
Term
Way to Resolve Enantiomers
Definition
1) chemical resolution
2)chromatography
Term
resolution
Definition
separation of enantiomers
Term
resolving agent
Definition
a chiral probe that is necessary for the resolution of enantiomers
Term
Chemical Resolution of Enantiomers
Definition
Term
polarimeter
Definition
measures the rotation of polarized light
Term
optically active
Definition
substances that rotate the place eof polarized light
Term
optical activity
Definition
rotation of the place of polarized light
Term
dextrorotatory
Definition
(d) rotating the place of polarized light clockwise
Term
specific rotation
Definition
a measure of a compound's ability to ratite the plane of polarized light **know formula
Term
optical purity
Definition
the specific toation of mixture of two eneantiomers, expressed as percentage of the specific rotation of one of the pure enantiomers
**Known formula
Term
levorotatory
Definition
(-) (l) rotating the place of polarized light counterclockwise
Term
Chromotography
Definition
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