Organic Chem Test #2




Enantiomer

Molecules that are not identical , but are mirror images

*Like a right hand is related to a left hand 

 

* results when a tetrahedral carbon is bonded to four dif substituents  



Chiral

A molecule that is not identical to its mirror image

 

*Molecule with NO plane of symmetry

*Most commonly a Carbon connected to four different groups 

 

 

Levorotatory 

Optically active molecules that rotate to the LEFT

 

*Given a  (-) sign

 

 

Dextrorotatory 

Optically active molecules that rotate light to the RIGHT

*Given a (+) sign

 

 

Equation for Specific Rotation 

 

 

[a]d = a/l x c

 

a=observed degrees

l= pathlength (dm)

c=concentration (g/cm3)

Rank the following highest to lowest: 

-H, -Cl, -Br, -CH3, -CH2OH, -NH2, -B, -O

-Br, -Cl, -O, -NH2, -CH2OH, -CH3, -B, -H

 

 

 

 

Diastereomer

Stereoisomers that are not mirror images

*Similar but not identical

 

* Have oppsosite configuration at some chirality centers but the same at others within the same chiral molecule 

 

 

Difference between Enantiomers and Diastereomers

enantiomers have opposite configurations at ALL chirality centers, diasteromers have opposite configurations at SOME (one or more) chirality centers but the same congfiguration at others.

 

 

Epimer

Diasteriomers that differ by configuration at only one chirality center

 

 

Meso Compounds

ACHIRAL (non-chiral compound) that contain chirality centers

 

 

Racemic Mixture

*50/50 mixture of enantiomers

 

 

*Reacts with non-chiral molecules to form racemic mixture of enantiomeric products.

 

 

 

Resolution

*Process of seperating racemic mixture

 

*employs chiral enantiopure resolving agents

 

*enantiopure reagents react with racemic mixture to form diastereomeric salts, which have diff physical properties and are seperated by crystallization

 

 

Constitutional Isomer

 

Compounds whose atoms are connected differently (same molecular formula)

 

 

Stereoisomer

compounds whose atoms are connected in the same order but with different arrangements in space

(enantomers, diastereomer [cis and trans]) 

 

 

Configurational Stereoisomer

configurational stereoisomer is a stereoisomer of a reference molecule that has the opposite configuration at a stereocenter (e.g., R- vs S- or E- vs Z-)

 

 

Prochiral Molecule

Molecule that can be converted from achiral to chiral  in a single chemical step (Changing a molecule with out affecting priority of other atoms)

 

*Have two faces Re (clockwise) Si (counterclock wise)

 

*Sp3 hybirdized prochiral atom can be Pro-S (replacement leads to a S chiral center) or Pro-R (replacement leads to R center)

 

What type of reaction is this?

 

[image]

Addition Reaction: 2 Reactants combine to form one product

What type of reaction is this?

 

 

[image]

Elimination Reaction: one reactant splits to form two products 

 

What type of reaction is this?

 

[image]

Substitution reaction: 2 reactants exchange substitients to form 2 new products

What type of reaction is this? 

 

 

 [image]

Rearrangement reaction: single reactant rearranges its bonds. Mirgration of sigma bonds from 1->3 would be called [1,3]
Types of Addition reactions:

 

Hydrohalogenation of alkene

 

 

Hydrogenation of alkene

 

 

Addition of Nucleophile to Ketones and Aldehydes

 

 

 

 

Types of elimination reactons:

Dehydration of Alcohols

Dehydrohalogenation of Alkyl halides (haloalkanes

 

 

Types of Substitution reactions

Esterification of Carboxylic Acid

 

Hydrolysis of Ester

 

 

Homolytic Bond Cleavage

*symmetrical cleavage

 

*Radical

 

*one bonding electron stays with each product

 

[image]

 

 

 

Heterolytic Bond cleavage

*unsymmetrical bond breaking

 

*polar

 

*two bonding electrons stay with one product

 

[image]

 

 

Radical Reactions

process that involves symmetrical bond-breaking and bond making 

 

 

 

Radical

a neutral chemical species taht contains an odd number of electrons and thus has a single, unpaired electron in one of its orbitals

 

 

 

Polar reactions 

* involves unsymmetrical bond breaking and bond making

 

*involve species that habe an even number ofelectrons 

 

 

 

Initiation step in methane chlorination

 

 

 

UV Light breaks weak CL-CL bond to give a few reactive chlorine radicals

 

[image]

 

 

 

 

Propagation step in methan chlorination

chloring radical collides with  methane molecule abstracting a hydrogen atom to give HCl and methyl radical (CH3)

* Methyl radical reacts furthar with Cl2 in second propagation step to give product chloromethane plus new chlorine radical, which repeats. 

*once initiated it becomes self sustaining / chain reaction

 

[image]

 

 

 

Termination of Methane chlorination

 

* When two radicals collide and combine to form a stable product. 

*Cycle is broke and chain is ended 

[image]

[Possible terminations]

 

 

What is a polar reaction?

* an electron pair is moved from electron-rich center(atom or bond) to electron-poor center.

 

 

 

 

 

 

 

 

 

 

 

 

Name 3 characteristics of a Nucleophile

NUCLEUS LOVING

 

* Negatively polarized electron rich atom

 

*form bond by donating pair of electrons to postively charges electron poor atom.

 

*Can be Neutral or Negative

 

 

 

Name 3 characteristics of an Electrophile

ELECTRON LOVING

 

*positively polarized, electron poor atom

 

*forms bond by accepting pair of electrons from nucleophile

 

*Can be neutral or positvely charged

 

 

What is the equation for Keq (equilibrium constant)?

 

product concentrations multiplied together divided by the reactant concentrations mulitplied together with each concentrations raised to the power of its coefficient

 

 

 

Gibbs free energy change (ΔG) equation


 What is the favorable outcome?

* equal to the free energy of the products minus the free energy of the reactants:

* A negative value is more favorable

*energy is lost by the chemical sytem and released =exergonic (negative value)

 

 

 

ΔG = GproductsGreactants

 

 

 

 

 

 

 


enthalpy, ΔH

The energy exchange between bonds and the surrounding during this process is measured by enthalpy, ΔH (ΔH is primarily determined by the energy required to homolytically break a bond, also bond dissociation energy)

 

 

Heat of formation

The total change in enthalpy during bond breaking and bond forming reaction is called heat of formation.

 

 

Is heat absorbed or released during bond breaking/and formation

Bond breaking (heat absorbed)
Bond forming (heat release)

 

 

What is degree of unsaturation and how can you figure it out?

*# of rings and/or multiple bonds in molecules

*One degree = one double bond or one ring

*2 degree= two double bonds, or one double bond and a ring, or two rings, or one triple bond

 

 

Formula: DU= C-1/2(H+X-N)+1

 

 

 

Is Cis or Trans alkenes more stable? why?

Trans- alkenes are more stable than cis alkenes because cis alkenes have larger steric strain from the substituents. Therefore, alkenes always prefer the trans-siomers

 

Which bond is stronger Sp3-sp3 or Sp2-sp3?

Bond Strengths: sp2–sp3 carbons bond is stronger than sp3–sp3 carbons bond.

 

 

 

Halogenation

Bromine and Chlorine add rapidly to yield 1, 2 Dihalides

 

Chorine = cis or trans

Bromine=Always trans

 

Halohydrin

1,2 disubstituted haloalcohol (X and OH)

 

 

[image]

 

What is this reaction?

Halohydrin reaction

 

 

Oxymercuration-demercuration

*Alcohol adds to the most substituted Carbon

 

*Reacts with (Hg[Oac]2) followed by addition of sodium borohydride

 

[image]

What is this reaction?

Oxymercuration-demercuration

*OH is added to the most substituted Carbon 

 

 

 

Hydroboration

*nonmarkovnikov addition of OH group (adds to least substituted)

 

*Uses addition of BH3, in THF solvent, followed by addition of H2O2(hydrogen peroxide), and NaOH(sodium hydroxide)

[image]

What reaction is this?

Hydroboration

 

*adds OH to least substituted carbon

 
 
 
Hydrogenation

 

*alkene converted to alkane 

*usually with (Pd/C) or platinum (Pt)

*Hydrogen added across the double bond

 

[image]

 

What reaction is this?

Hydrogenation

 

turns alkene to alkane with adding Hydrogen

 

 

Oxidation

*Decreases electron density on carbon by 

1. forming a carbon bond with O, N, or X(halogen)

2. Breaking a Carbon bond with Hydrogen 

 

 

Reduction

*Increses electron density on carbon by
1.Forming carbon bond with Hydrogen

2.Breaking carbon bond with [O, N, and halogen] 

 

 

Dihydroxylation

*add 2 hydroxyl  groups using  OsO4 & H2O2

[image]

What reaction is this?

 

 

Dihydroxylation

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