Organic Chemistry Flashcards
Suffixes -ene and -yne signify
Double and triple bonds respectively
Alkenes are listen before alkynes
Stereocenter definition
Is an atom where whine two substitutients switch positions, a new stereoisomer is formed.
Both sp3 carbon ( chiral center) and sp2 carbon if the Allen’s can be classified E/Z or cis/trans
Diastereomers definition
Stereoisomers that are not mirror images (they are the same) and contain at least two stereo centers in which one or more ( not all) of the stereocenters on corresponding carbon atoms are in opposite configurations.
Have at least two stereocenters
Conformational isomer
Different forms of the same molecule that are generated as atoms rotate their bonds
What molecules rotate plane polarized light and how?
Enantiomers by the same magnitude but in opposite directions.
Racemic mixtures have a rotation of 0 because they have equal amount of each enantiomer
What is number of stereoisomers?
2^n
Where n is a number of stereocenters
What is an epimer?
A type of a diastereomer that differs in configuration at only one stereocenter
Tautomerization is
Type of isomerization that involves the transfer of hydrogen from one position to another within a molecule and movement of a double bond to an adjacent atom.
Usually involves a Keto form (C=O) as the original form where the enol is the minor tautomer.
Classified as constitutional isomers because a bond is broken
Imine group
C=N
What overlap does pi bond?
Side to side overlap
What overlap does a sigma bond have?
End to end
What atoms can freely rotate around the bond?
Only sigma bond (single)
Bond length is inversely proportional to what ?
Bond strength
NMR splitting of hydrogens
Related to number of hydrogens covalently bonded to carbons (C-H)
NMR characteristics
Protons shielded by nearby electrons have smaller chemical shifts ( upfield).
Deshielded protons such as those near electronegative atoms , have larger chemical shift ( downfield)
HPLC characteristics
High performance liquid chromatography
Technique to separate, quantify and characterize components of mixture.
Mobile phase (hexane) migrates through a stationary phase ( silica) and carries the compounds of interest with it.
Retention time = time to travel the column. Longer time = greater affinity for the stationary phase and less affinity for the mobile phase).
Specific rotation for isomers
Diastereomers have different magnitude and may differ in direction.
Enantiomers have same magnitude but opposite direction.
Racemic mixture composed of 50:50 Enantiomers which have 0 rotation.
Conformational isomers have same rotation
Clockwise rotations are + while CCW are -
Characteristics of constitutional isomers?
Known as structural
Same molecular formula
Different connectivity of atoms
Usually have different physical properties (MP, BP..)
What are the anomers?
Type of diastereomer that differed in configuration at only one the anomeric carbon ( a carbon that has two bonds to oxygen)
Note: alpha and beta designations in a sugar means different orientation of the hydroxyl group at the anomeric carbon
Difference between diastereomer and Enantiomers
Enantiomer differ in configuration at every stereocenter while diastereomer at only one stereocenter
Enantiomers characteristics
Mirror images (rotate 180 degrees)
All stereocenters have opposite configurations
Alkanes characteristics
Composed only from C and H and lack pi bonds.
Leastr reactive because of nonpolar bonds
Cycloropane is the most reactive among all other alkanes due its increased ring strain.
Higher molecular weight mean
Higher BP ( but it doesn’t impact chemical reactivity)
R and s configurations
In SN2 reaction when an electrophile is a chiral center then
Its stereochemistry will be inverted by the reaction ( R to S or vice versa) and S have a wedge
Conformational relationships characteristics
Eclipsed = 0 degrees and 120 degrees results in higher energy and 0 degree has a higher energy than 120 degrees.
Staggered = 60 degrees and 180 degrees results in lower energy
What does it mean stereospecific?
When stereoisomers undergo the same reaction and each give only one specific stereoisomer of the product.
SN2 reaction are stereospecifiwc while SN2 are not
What AA has several Diastereomers?
Isoleucine
Degree of unsaturation
Each ring or a pi bond counts as one degree of unsaturation
A stable carbocation in SN1 reaction has
Are fastest to react
Then secondary and primary
Carbocations and carbanions stability
What is a steric hindrance?
When a nucleophilr and electrophile bump into one another rather than reacting
Alkyl halides reactions
Tertiary - SN1 high steric hindrance
Secondary - SN2, very rare SN1 (with weak base nhcleophile)
Primary - SN2 low steric hindrance
The most nucleophilic compound is one that
Has the lowest electronegativity
The most nucleophilic compound is one that
Has the lowest electronegativity
The most nucleophilic compound is one that
Has the lowest electronegativity
When inductive effect occurs?
When electron density is donated through sigma bonds.
Carbocations are stabilized by electron donating group because they donate electrons to the positively charged carbon.
They are distabilized by electron withdrawing groups because they pull electrons away creating two adjacent charges
In SN2 reactions if the electrophile is a chiral center than
Its stereochemistry will be always inverted ( configuration)
Alcohol groups characteristic
Primary is least statically hindered, the secondary and tertiary is the most hindered.
Primary - SN2
Secondary -SN1 or SN2
Tertiary- SN1
Primary are more acidic than secondary and tertiary
Primary acts as a nucleophile
What is Fischer esterification?
Acid catalyzed condensation of a carboxylic acid and an alcohol into an ester.
String acids can donate their protons to other molecules to catalyze a reaction. Acidic origination enhances the rate of esterification.
1) formation of a resonance stabilized intermittent due to a protonation of the carbonyl oxygen
2) enhances/ increasing carbonyl
Electrophilicity and decreasing the nucleophilicity
3) protonation of a hydroxyl convert into a good leaving group ( like water)
Good leaving groups are
Logarithmic scales
One step is a 10 fold change, two steps is a 100 fold change, three steps is a 1000 fold change
Differences between kinetic and thermodynamic products
Kinetic: higher in energy, less stable, minor product
Thermodynamic: lower in energy, more stable, major product
What hybridization do substrate and products of an SN1 reaction usually have.
Sp^3 with a carbocations of sp^2
Characteristics of carbocations during SN1?
Tertiary provide the highest rate of a reaction and have the greatest stability while primary slows the rate and stability
While nucleophile doesn’t affect the rate of a reaction!!!
How to select the event electrophile for an SN2 reaction?
This reaction occur fastest for less statically hindered carbon electrophiles ( like primary structures). Carbon should be bonded to a halogen group.
Strong and weak nucleophile characteristics
Most sterically hindered = slow reaction and vice versa
What solvents are used to promote SN2 and SN1 reactions?
Polar aprotic solvents that lack of hydrogen bonding
Imine functional groups characterized by
Carbon nitrogen double bond
Amide functional groups charactwtiatics
Carbonyl bonded to N
Imide functional groups
N is bonded to two carbonyl on the sides
More resonance forms the compound has means
More stable it is
What helps to compound it be more stable?
Increased delocalization of electron density, conjugated pi systems help stabilize carbanions by delocalizing the charge
What is decarboxylation?
Removal of a carbonyl group with the release of CO2
