Organic Chemistry Flashcards
Characteristics of a good nucleophile
- basicity and electronegativity
strong base
weak electronegativity (opposite of EN)
increase left in the periodic table
so C- > N- > O-
Characteristics of a good leaving group
- in terms of basicity
- how it relates to nucleophilicity
Lots of shells - down the periods
weak base - conjugate of a strong acid
opposite of nucleophilicity
In nucleophilic substitution, given that there are two nucleophiles, which one will leave and which one will remain?
the stronger nucleophile will remain and the weaker one will leave
When would alcohol act as a nucleophile versus an acid?
has EWG or EDG
Ways to make alcohol into good leaving groups
Protonation or sulfonation
How to protect the alcohol and prevent it from acting as an acid
sulfonation - make into a methylate or tosylate
How to determine the reactivity of carbonyls
more positive the carbonyl, more reactive it is
more positive it is, more likely it will get attacked
Sigma bonds
- where the electrons are localized
- strength of the bond, stability, and energy released
electrons are localized directly between the nuclei
very stable, lots of energy released, low energy level
pi bonds
- where the electrons are localized
- strength of the bond, stability, energy released
- atoms that form pi bonds
not close to the nucleus, top and bottom
reactive, weaker bond, reactive
- O, S, P tend to form pi bonds
If a bond has more “s” character, what does it say about the length, strength, and stability?
shorter, stronger, and more stable
According to the VSPER theory, how are the angles determined?
angles that minimize the repulsive forces between the atoms
How to lone pairs and pi electrons distort the predicted bond angles?
lone pairs and pi electrons require more room than bonding pairs, so they distort the predicted bond angles
How many atoms are the delocalized electrons shared by?
shared by 3 or more atoms
T/F: resonance only results from pi bonds and lone pairs
T
What is resonance energy?
the difference between the energy of the real molecule and the energy of the most stable Lewis structure
What are the rules about the number of atoms, unpaired electrons, and resonance atoms in the rules of drawing resonance structures?
atoms are where they were
the number of unpaired electrons must remain the same
the resonance atoms must lie in the same plane
What is the stability of the resonance structure determined by?
Determined by a resonance structure that contributes the most - the most stable resonance form with the lowest formal charge with less charge separation in the molecule
How does the stability of the conjugate base relate to the acidity of the acid?
More stable the conjugate base, more stronger the acid
Requirements to be “aromatic”
cyclic
planar
4n+2 number of pi electrons
What does it mean when a molecule is aromatic?
increased stability of a cyclic molecule due to the electron delocalization
Structural isomer
bond to bond connectivity
Eclipsed vs. fully eclipsed conformer
fully eclipsed - steric functional groups are eclipsing one another
gauche conformer
steric functional groups are right next to each other front and back
anti-staggered conformer
steric functional groups are anti to one another front and back
what is a relative configuration?
two molecules are said to have the same relative configuration if the orientation of all the substituents are the same except for one substituent.
How do R and S enantiomers differ?
they differ on how they rotate the plane polarized light
what is a plane polarized light
light with electric fields oriented in the same direction
what does it mean when a compound is optically active?
the compound rotates the plane polarized light to a certain degree. in other words, light with electric fields oriented in the same direction is rotated to a certain degree and direction.
what is compound’s observed rotation?
Observed rotation includes the degree and direction of rotation of the electromagnetic field
what is a specific rotation?
a standardized form of observed rotation that is calculated from the observed rotation and experimental parameters.
what is an optical purity?
the ratio of actual rotation to the rotation of pure sample
what are diastereomers?
connectivity? formula? mirror images? same compounds?
same connectivity, same formula but not mirror images; NOT the same compounds
Do diastereomers differ in physical and chemical properties?
different compounds - have different physical and chemical properties
what is the maximum number of optically active isomers that a single compound can have given an “n” number of chiral centers
the maximum number of optically active isomers a compound can have given “n” chiral centers is 2^n
What are meso compounds?
are they chiral? do they rotate plane-polarized light?
internal mirror images
achiral, do not rotate plane-polarized light
What are epimers?
epimers are diastereomers that differ in configuration at only one chiral center
what are anomers?
anomers are cyclic diastereomers - when a ring closure occurs at an epimeric carbon
What are cis/trans isomers?
special diastereomers that exist due to multiple bonds or a ring structure
do cis and trans isomers have different physical properties?
cis and trans isomers have different physical properties because cis has a dipole moment whereas trans does not
trans isomers stick more easily; thus, have higher mp and bp than cis isomers
how to determine cis or trans isomers (E or Z)
determine high or low priority groups on each carbon, then identity how the high and low priority groups are distributed among the different carbons
same side: Z
opposite sides: E
what are the different kinds of diastereomers?
configurational diastereomers - epimers
cis/trans diastereomers - cyclic or multiple bonds
in order of reactivity:
amides, aldehydes, ketones, anhydrides, esters, carboxylic acids, acyl halides
how to determine this reactivity
acyl halides > aldehdes ketones > anhydrides > esters > carboxylic acids > amides
by examining the reactivity of the leaving groups; more stable the leaving group is in solution, more likely the nucleophilic substitution will take place
what condition is needed for hydrolysis of amides to make carboxylic acids?
extreme condition is needed
high temperature, strong acid
this is unlikely to occur in biological systems
what is important in achieving transesterification?
it is important to add excess alcohol you want to substitute in
in aldehyde and ketone tautomerization, which tautomer form is more stable?
keto (aldehyde/ketone) is more stable form because the enol is weakened by the electronegativity of the oxygen
what can tautomers catalyzed by?
what happens during tautomerization?
acid or base
deprotonation of the alpha carbon and protation of the carbonyl carbon
Describe the strength difference between NaBH4 and LiAlH4
Only LiAlH4 is strong enough to fully reduce carboxylic acids,esters, and acetates to alcohols
But both can reduce aldehydes and ketones, and acyl halides to alcohols
how to form carboxylic acid from acyl chloride
acyl chloride + nitriles (CN-), becomes, cyanohydrin
cyanohydrin is converted to carboxylic acid when exposed to water and acid
what’s more stable enamine or enols?
enamines are more stable than enols as nitrogen is less electronegative and less electron withdrawing than oxygen
How are enamines and imines formed?
acid catalyzed addition of amines
depending on if there is hydrogen available on the amine, it will be imine or enamine. Imine if there is hydrogen available on the amine
can there be a tautomerization between imine and enamine
only when the original amine is primary. this happens on the nitrogenous bases of nucleotides
when carboxlic acid gets reduced to alcohol, what does it become first?
gets reduced to aldehyde, then alcohol, then to alkene, to lakane
when alcohols get oxidized, what do they become first?
alcohols become oxidized to aldehydes then to carboxylic acids
Reduction of carboxlic acids and esters by NaBH4
No reaction
reduction carboxylic acids by two equivalents of LiAlH4
alcohol
how many LiAlH4 equivalents are needed to reduce carboxlic acids to alcohol?
2
how many LiAlH4 equivalents are needed to reduce aldehyde and ketone to alcohol?
1
how many NaBH4 equivalents are needed to reduce aldehde and ketone to alcohol?
1
when is hydrogen electronegative versus electropositive in a molecule?
electronegative when bonded to anything left of boron on the periodic table
electropositive when bonded to anything right of the carbon on the periodic table
MnO4 2-, CrO4 2-, Cr2O7 2-
vs.
PCC
PCC is a gentler oxidizing agent so it’ll only oxidize primary alcohol to aldehde and secondary alcohol to ketone
permanganate, chromate, and dichromate are strong oxidizing agents so they will oxidize primary alcohol all the way to carboxylic acids
what happens when phosphoric acid is heated?
forms phosphoric anhydrides
phosphoric acids reaction with alcohol
phosphoric acids react with alcohol to form esters
oxidation
increasing bonds to oxygen, halogens, loss of C-H bonds
losing electron density
reduction
increase in bonds with hydrogen or carbons. Loss of bonds to oxygen or halogen
can tertiary alcohol be oxidized?
no
why is it easier to decarboxylate when the beta-carbon is a carbonyl?
because the anion intermediate is resonance stabilized or the acid forms a more stable cyclic intermediate
