OChem-Mcat review

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Vinyl-
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*are monosubstituted ethylenes

 

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allyl-
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*are propylenes substituted at the C-3 position
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Methylene-
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*refers to the -CH2 group as a substitute

 

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isomers
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*chemical compounds that have the same molecular formula but differ in structure
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Structural Isomers
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*compounds that share only their molecular formula

*often have very different properties

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Stereoisomers
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*compounds that differ from each other only in the way that their atoms are oriented in space

*Includes:geometric isomers, enantiomers,diastereomers, and meso compounds

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Geometric Isomers
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*compounds that differ in the position of substitutents attached to a double bond

 

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Chirality
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*an object that is not superimposable upon its mirror image

(example right and left hand)

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Enantiomers
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*Chiral objects that are nonsuperimposable mirror images

*refers to a pair of objects

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relative configuration
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*of a chiral molecule is its configuration in relation to another chiral molecule
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absolute configuration
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*of a chiral molecule describes the spatial arrangement of these atoms or groups
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Diastereomers
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*stereoisomers that are not mirror images
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Meso compound
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*contains a plane of symmetry, and is not optically active
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Conformational isomers
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*compounds that differ only by rotation about one or more single bonds

*(basically the same compound in a slightly different position)

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Staggered (anti) conformation

 

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*most stable conformation

*when two methyl groups are oriented 180? from each other

*min energy, min repulsive steric interactions

 

 

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Gauche conformation

(staggered)

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*occurs when the two methyl groups are 60? apart

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Eclipsed conformation
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the two methly groups are 120? apart and overlap with the H atoms on the adjacent carbon
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Totally eclipsed
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*when the two methyl groups overlap

*highest energy state

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What type of strains do cycloalkanes have?
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1.) angle strain

2.)torsional strain

3.) nonbonded strain

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Physical properties of alkanes
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*as MW increases so does MP, BP, and density

*at room temp, straight chains w/ C1 to C4 are gas

*at room temp, straight chains w/ C5 to C16 are liquid

*longer chains are wax or harder solid

*branching lowers BP, and MP

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Combustion
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*Reaction of alkanes with molecular oxygen to form carbon dioxide, water, and heat

 

Rxn: CnHm + 5O2 → 3CO2 + 4H2O + heat

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Pyrolysis

(AKA Cracking)

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*Break Down of a molecule by heat

*used to reduce the ave. MW of heavy oils and to increase the production of the more desirable volatile compounds

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What is a nucleophile
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Nucleus loving
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How does basicity effect a nucleophile?
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*If they have the same attacking atom, then the stronger the base = greater strength

Ex]

RO>HO>RCO2>ROH>H2O

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How does Size and polarizablity effect nucleophiles
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*in a protic solvent and when attacking atoms differ, large atoms tend to be stronger

CN>I>RO>HO>Br>Cl>F

*In aprotic solvents, strength is related to basicity

F>Cl>Br>I

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Leaving group
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*best are those that are weak bases

–(these can accept an electron pair and dissociate to form a stable species)

ex] I>Br>Cl>F

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SN1 reactions
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*Unimolecular nucleophilic substitutions

*rate is dependent upon only one species, formation of Cation

~*Mech*~

Step 1.) dissociation of molecule to form carbocation

Step 2.) Attack of Nucleophil on Carbocation

*Highly substituted cations are more stable

 ~~**Favored in polar protic solvents

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SN2 reactions
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*involves a nucleophil pushing its way into a compound while simultaneously displacing the leaving group

*rate is determined upon substrate and nucleophile

 

~*Favored in polar aprotic solvents

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what effects whether a reaction will be

SN1 or SN2 ?

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*Sterics, nucleophil strength, leaving group ability, reaction conditions, and solvent effects.
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Degree of Unsaturation

(The number (N) of double bonds)

 

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=.5 (2n+2-m)

*for the compound CnHm

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Physical properties of Alkenes
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*MP and BP increase w/ MW

*Trans- have higher MP (due to symmetry) and Lower BP (due to less polarity) than Cis

 

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Unimolecular elimination (E1)
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*Two-step process

*rate is dependent on substrate

*Elimination of a leaving group, then proton is removed by a base forming a double bond

~*Favored Highly polar solvents, highly branched carbon chains, good leaving groups and weak nucleophiles in low concentrations

 

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Bimolecular Elimination (E2)

 

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*Occurs in 1 step.

*rate is determined by both substrate and the base

*strong base removes proton while halide leaves forming double bond

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Huckel’s rule
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*used to determine aromaticity

*4n + 2 pi electrons = # carbons

~* Solve equation for n, if n is a nonnegative integer compound is aromatic

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Meta-
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*1,3 disubstituted compounds
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Ortho-
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*1,2 disubstituted compounds
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Para-
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*1,4 disubstituted compounds
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Physical properties of Aromatic Compounds
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*Similar to other hydrocarbons however the Delocalization stabilizes the molecule making it unreactive

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Physical properties of Alcohols
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*Higher BP (due to H-bonding)

;

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Physical Properties of Ethers
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*DO NOT UNDERGO H- BONDING

*Low BP (compared to Alcohols)

*slightly polar

*often used as solvent (are unreactive to most organic reagents)

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Physical properties of Aldehydes and ketones
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*Higher BP than alkanes due polar group (but still lower than alcohols)

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Physical properties of carboxylic acids
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*Are polar

*higher BP than alcohols and increase w MW

*Acidity;is due to carboxylate anion

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Properties of amines
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*BP is b/w alkanes and alcohols

*are basic and readily accept protons

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Extraction
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*transfer of a dissolved compound from one solvent into another in which it is more soluble

*impurities are left behind in the first solvent

*Both solvent are immisible

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Filtration
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*used to isolate a solid from a liquid

;

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Recrystallization
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*process in which impure crystals are dissolved in a minimun amount of hot solvent. Once cooled the crystals reform leaving impurities in the solvent

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Sublimation
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*Occurs when a heated solid turns directly into a gas w/o an intervening liquid stage

*most impurities will not sublime easily

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Distillation
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*The separation of one liquid from another through vaporization and condensation

1)simple, 2)Vacuum, 3) fractional

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