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All main topics / Chemistry / MCAT

MCAT Orgo Rules and Properties (47 Cards)

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Functional Group Prefixes and Suffixes
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Ketone and Aldehyde Properties
-positive alpha-carbon
-acidic beta-carbon
-elevation in BP from alkane due to dipole
-BP not up to alcohol due to no hydrogen bonding
-aldehydes more reactive than ketones. Why?
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Alcohol Properties
-hydrogen bonding (# hydroxyl groups)
-high boiling points
-weakly acidic (pKa = 10phenol to 16water)
-6-carbon rule = alcohols with C-chains > 6 are no longer soluble
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Criteria of Aromaticity
1. Huckel's Rule (4n+2)
2. Planar and cyclic
3. Every atom delocalized
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Alkene polarity
Trans alkenes have higher melting points (symmetrical) and lower boiling points (less likely to be polar).

SP3 carbons donate electrons to SP2 carbons - orbitals more s character, closer to nucleus, more stable.

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Oxidation of a double bond
1. KMnO
     - mild conditions (vicinal diols)
     - extreme conditions (carboxylic acids)

2. Ozonolysis
     - mild conditions, reducing Zn/water environment (ketones/aldehydes)
     - extreme conditions, oxidizing environment

3. NaBH or LiAlH

4. Peroxyacetic acids = CHCOH or MCPBA (epoxide formation)

5. Hydroboration (NaBH, peroxide)
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How do you control for E2, versus SN2?
-bulky, stronger base
   (NOT -CN or -I or even -OH, but -OR)
-substrate steric hindrance
   (why? hydrogen removal rather than )
-HEAT

Key Points
bulky base = E2
heat = E2
3*C substrate = E2
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Chlorination energy diagram
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How do you find the reactivity of hydrogens?
Find the amount of product formed per hydrogen and compare.
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Hammond Postulate
Related species that are similar in energy are also similar in structure. The structure of the transition state resembles the structure of the closest stable species.

-transition state for endothermic rxns resembles the product, exothermic the reactant.
-bromination transition state is closest to product. Thus reactivity very closely related to end-product stability (i.e. stability=speed).
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Bromination energy diagram
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Physical properties of alkanes
*chain length; increase
   -bioling point
   -melting point
   -density

*branching; decrease
   -boiling point
   -density

*melting point and branching - determined by how symmetrical the molcule is; packing density. Easier to stack, more dense, higher melting point.
Tags: physical properties
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Factors affecting substitution
1. Basicity of Nu
       RO- > HO- > RCO > ROH > HO
2. Polarizability (size) of Nu
       CN- > I- > RO- > HO- > Br-
3. Solvent
      -protic = solvate the leaving group.
      -polar = solvate the intermediate.
4. Leaving group (base weakness)
5. Substrate (charge delocalization)
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Relative versus absolute configuration
Relative = experimentally determined, x-ray crystallography; always reversed in SN2 reactions (D/L; +/-).

Absolute = determined by priority group orientations; not necessarily reversed in SN2 reactions (R/S).
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SN1 reaction
-good leaving group
-stable substrate, bulky Nu.
-favored in polar, protic solvents
-two steps (two transition states)
-rate=k[RX] ; first order kinetics
-racemic products
-rate limiting step is the first step = formation of the carbocation.
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In free-radical halogenation, why is bromine more selective than chlorine?
1. Slower reaction
2. Transition state more dependent on product stability (endothermic)
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What is the difference between a transition state and an intermediate?
Intermediate = stable, relative minimum, stable species.
Transition state = theoretical, unstable, relative maximum, for mechanism solely.
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SN2 reactions
-Nu > leaving group
-favored in aprotic POLAR solvents
-r=k[Nu][RX] ; second-order kinetics
-reverse relative configuration
-no steric hindrance in substrate, small Nu.
-trigonal bipyramidal transition state (sp)
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SN1 energy diagram
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SN2 energy diagram
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Adding s-AOs to form -MOs
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s+s Energy diagram
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p+p Energy diagram
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sp hybridization (energy diagram)
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hybrid orbitals
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hybrid orbitals
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Adding p-AOs to form and -MOs
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Isomers
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Butane Conformation PE
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Enantiomers
Non-superimposable mirror images.

Same physical properties except rotation of polarized light
Same chemical properties except with chiral molecules
Tags: Isomers
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Diastereomers
Similar - Large in physical and chemical properties.
Tags: Isomers
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Functional Group Priorities
Carboxylic Acids Carbon
Ester Es
Amide A Dignified
Nitrile Neutral
Aldehyde Atom
Ketone Kind
Alcohol And
Amine Amazing
Ether En
Double-bond Dirty
Triple-bond Threesomes
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Common Alkanes
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Common Alkane Substituents
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Structural (Constitutional) Isomers
Same molecular weight and molecular formula.
Different atomic connectivity.
Different physical properties.
Different chemical properties.

*Number of isomers per CH formula.
Tags: Isomers
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Stereoisomers
Same atomic connectivity, but different arrangement in space.

1. Conformational
2. Geometric
3. Enantiomers
4. Diastereomers
5. Meso compounds
Tags: Isomers
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Conformational Isomers (Conformers)
Do not need bond breaking to convert from one to another.
i.e. rotation about a bond.

Same physical and chemical properties.
Tags: Isomers
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Configurational Isomers
Require bond breaking to interconvert.

1. Geometric
2. Optical
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Geometric Isomers
Stereoisomerism at a double bond or cycloalkane.
i.e. cis or trans, (Z) or (E)

Different properties when difference in net polarities
Tags: Isomers
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Specific Rotation of Polarized Light
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Optical Isomers
Configurational isomerism involving single bonds.

1. Diastereomers
2. Enantiomers
3. Meso compounds
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Elimination reactions - important points
- more substituted bond product favored
- trans isomer favored
- anti hydrogen removed by base
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Oxidation
* losing hydrogens
* gaining double bond
* gaining oxygen
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Mechanism of catalytic hydrogenation of a double bond
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Lewis acids versus bases
* Lewis acid = e acceptor.
* Lewis base = e donator (benevolent).
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Markovnikov's Rule
the goal is to produce the most stable carbocation in alkyl halide addition to double bonds.
addition of the halogen to the more substituted carbon in the double bond.
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Alkyne physical properties
* higher boiling points than alkenes
* more polarized than alkenes
* internal alkynes BP > terminal alkynes BP
* terminal alkynes fairly acidic (PKA~25) due to high s character (50%), stabilize negative charge.
Tags: physical properties
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Flashcard set info:
Author: jmilber
Main topic: Chemistry
Topic: MCAT
Published: 24.06.2010
Tags: MCAT, chemistry
 
Card tags:
All cards (47)
bonding (7)
Isomers (8)
isomers (2)
physical properties (3)
rxns (1)
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