Organic Chemistry Flashcards
conjugation
3 or more adjacent pi orbitals
aromatic compounds
have a planar structure developed
n+2 is the number of pi electrons. n can be any integer
How can you determine what is a stronger acid?
look at the stability of the conjugate base
How can you determine a stronger base?
look at the stability of the conjugate base, see what is a better acid and do the opposite
What is a stronger acid: carboxylic acid or phenol?
carboxylic acid since you can make resonance structures with the negative oxygen
carboxylic acid has a very stable conjugate base, making it a strong acid
Thermodynamic characteristics of alkanes
low melting/boiling points since they only have london dispersion forces between them
volatile
refers to molecules with low boiling points
Two ways to form alkyl halides
heating diatomic molecules to form free radicals, then the free radical will react with the hydrocarbon
or, hydrohalogenation
hydrohalogenation
addition of a halogen atom to the double bond of an alkane
Why are alkyl halides so reactive?
they possess a great leaving group (halide) and they pull electrons from carbon making carbon electrophilic
phenyl
benzene ring
How can you reduce an alkene to an alkane?
through hydrogenation, add more hydrogen
isomers
molecules that share the same formula but differ in structure
structural isomers
also called constitutional isomers
connectivity is different
have to break bonds to convert between structural isomers
tautomers
structural isomers that interconvert with one another and exist together in equilibrium
connectivity differs, this is not resonance!
example of tautomers
keto-enol tautomer
conformational isomers
how single bonds are arranged in space
rotation around a single bond can convert between conformational isomers
where should bulky constituents be placed in the most stable chair conformation?
they should be placed equatorially
geometric isomers
a type of configurational isomer
configuration around a double bond
cis/trans or E/Z
E configuration
highest priority groups are on opposite sides of the double bond
Is Z the same as cis?
no
Z refers to highest priority groups, while cis refers to the same groups. Nitpicky detail
Z configuration
highest priority groups are on same side of the double bond
enantiomers
a pair of non-superimposable mirror images
How can two molecules with multiple chiral centers be enantiomers?
if the molecules have different configurations at the same location
ex: RRS / SSR
racemic mixture
mixture of 50/50 enatiomers cannot rotate light
What are some ways to separate enatiomers?
use chiral chromatography
interactions with a chiral ligand
What is the D/L orientation of most amino acids?
L
What is the D/L orientation of most saccharides?
D
What is the relationship between D/L?
they are enantiomers
diastereomers
have different configurations at some but not all locations
ex: RRR / SSR
epimers
stereoisomers that differ at just one chiral center
ex: RRS / RRR
meso compounds
have an internal plane of symmetry which makes them achiral
Can meso compounds be enantiomers?
no, since they are achiral
Where do you start numbering a Fischer projection of a carbohydrate?
at the top carbon
Where do you start numbering a Haworth projection of a carbohydrate?
at the anomeric carbon
Where does the anomeric carbon come from?
it is the original carbonyl carbon in the aldose/ketose that was attacked by an -OH group
Where does the oxygen that attacked the carbonyl group to cyclize end up on Haworth projection?
the oxygen ends up in the ring
What do aldoses lead to?
hemiacetal anomeric carbons
What do ketoses lead to?
hemiketal anomeric carbons
Is the anomeric carbon directly attached to two oxygens?
yes
furanose
a cyclic carbohydrate with a 5 membered ring
pyranose
a cyclic carbohydrate with a 6 membered ring
can furanoses have 6 carbons?
yes, that would be a hexose furanose
furanose just tells us about the ring NOT about the number of carbons
where does the right side of Fischer projection point in Haworth projection?
down
alpha anomer
anomeric hydroxyl group points down
beta anomer
anomeric hydroxyl group points up
mutarotation
moves between beta and alpha anomers
need to break a bond for mutarotation to occur
What determines melting points and boiling points?
intermolecular interactions
More -OH groups results in what?
higher melting point
Water’s pKa
14
How can you make alcohols more acidic?
add electron withdrawing group
then, when the -OH proton is removed the conjugate base can better distribute the negative charge
How can you make alcohols less reactive?
add electron donating group
EDG will make the conjugate base less stable, and therefore the alcohol is less likely to react
-al
aldehyde
-one
ketone
-oic acid
caboxylic acid
What can primary alcohols become?
primary alcohols can become either aldehydes or be further oxidized to carboxylic acids
What can secondary alcohols become?
secondary alcohols can be oxidized to ketones
What can tertiary alcohols become?
3º alcohols cannot be further oxidized
PCC
a weak oxidizing agent
can turn hydroxyls into carbonyl
Example of stronger oxidizing agents
molecules with Cr and Oxygen
or molecules with a metal and oxygen
Alcohols in synthesis reactions
if we want to protect the alcohol, need to use a protecting group
protecting groups
silyl ethers, mesylates, and tosylates
How can mesylates and tosylates be used?
they can act as either protecting groups or make a species into a better leaving group
How can you use alcohols to protect groups like aldehydes?
use alcohols to convert the carbonyl into a non-reducable acetal group
nomenclature for positions on phenol
ortho is next to the -OH group
meta is in the middle
para is directly across from the -OH group
quinone
an oxidized version of a diphenol
not aromatic
ubiquinone
coenzyme Q
an important electron receptor in the ETC
can carry up to two electrons
acetone structure
a ketone with two methyl groups
What is a good solvent for SN2 reactions?
aldehydes and ketones since they are polar aprotic solvents
What has a higher melting point, alcohols or ketones?
alcohols cause they can participate in more H-bonding
Where is the alpha carbon?
the alpha carbon is adjacent to the carbonyl carbon
What is more acidic, aldehyde or ketone?
aldehyde
aldehydes have a more stable conjugate base because a ketone’s methyl group acts as a EDG, which makes conjugate base less stable
How can you deprotonate alpha carbon of ketone?
need a very strong base
Beta-dicarbonyls
more acidic at their middle alpha carbon due to resonance
can you oxidize ketones?
no
How can you oxidize aldehydes?
need a strong oxidizing agent
PCC will NOT be strong enough
What are common nucleophilic attackers of carbonyl groups?
water
alcohols
cyanide
What forms when alcohol reacts with ketones?
form a hemiketal
alcohols tend to keep reacting and form a ketal
What forms when alcohol reacts with aldehydes?
form a hemiacetal
alcohols tend to keep reacting and form a acetal
What forms when aldehyde is reacted with amine?
imine
acetic acid structure
carboxylic acid with methyl
formic acid structure
carboxylic acid with hydrogen
simplest carboxylic acid
inductive effect
highly electronegative species pull ED down the molecule
can stabilize conjugate base
what is more important inductive effect or resonance?
resonance
saponification
mix triglyceride with strong base
break ester bonds in triglyceride
form carboxylate anion that forms a salt with a nearby metal cation
DIBAL
weak reducing agent
decarboxylation
carboxyl group is lost at CO2
favored at high temps
biochemical example of decarboxylation
pyruvate to acetyl-CoA
Hell-Volhard-Zelinsky Halogenation overall
carboxylic acid is converted to an alpha-halo acid
still have a carboxylic acid, just with a halogen on the alpha carbon
Hell-Volhard-Zelinsky Halogenation steps
acyl halide is made from carboxylic acid
tautomerization occurs and forms carbon double bond
halogen attacks the double bond
results in halogen attached to alpha carbon of an acyl halide
add water to convert the acyl halide to a carboxylic acid
What are cyclic amides called?
lactams
What are cycle esters called?
lactones
Boiling points of amides
lower than carboxylic acids and alcohols
transesterfication
switches ester with a new alcohol
acid-catalyzed amide hydrolysis
hydrolyze amide to form carboxylic acid and amine
this is what happens in peptide bond hydrolysis
List the reactivity of carboxylic acid derivatives from least to most reactive
Carbonate anion Amide Carboxylic acid Ester Anhydride Acyl halide
Acyl halide
halogen attached to a carbonyl group
What does the reaction rate depend upon in SN1 reactions?
just the concentration of the substrate
What does the reaction rate depend upon in SN2 reactions?
the concentration of the substrate and nucleophile
How many steps is an SN1 reaction?
2 steps
First, the carbocation is formed and then the nucleophile attacks
How many steps is an SN2 reaction?
1 step
simultaneous nucleophilic attack and leaving group departure
What is the rate limiting step of an SN1 reaction?
the formation of the carbocation
Stereochemistry of SN1 reactions
since the nucleophile can attack the carbocation at either empty p-orbital, a 50-50 racemic mix of enantiomers is produced
Stereochemistry of SN2 reactions
Due to the backside attack, the sterochem is inverted
Would a 3º substrate be likely to react through SN1 or Sn2 mechanism?
SN1
the 3ºcan stabilize the carbocation and the 3º creates too large of sterics for the SN2 reaction
What solvent should we use for SN1 reaction?
polar protic solvent
ethanol, water, methanol
What solvent should we use for SN2 reaction?
polar aprotic solvent
acetone, DMSO, and DMF
Fisher esterification
turn carboxylic acid into ester with a reaction with an alcohol
reversible through hydrolysis
Imine formation
react ketone and amine in acidic conditions to form imine
E1
two steps and is driven by carbocation formation
E2
only has one step and need a very strong base to occur
Nucleophilic addition
nucleophile adds itself to electrophile without kicking another group off
What is normally the result of nucleophilic addition?
a hemiacetal or hemiketal
What is needed for nucleophilic addition to take place?
a substrate with a double bond or triple bond
How does base catalysis work?
deprotonate the nucleophile to make it even more nucleophilic
What is another example of tautomerism besides keto-enol?
imine to enamine
Enol
C-C double bond with hydroxyl group attached
How does keto-enol tautomerism generally work?
deprotonate the alpha-carbon to form a C-C double bond
Under what conditions will an enolate form?
basic conditions
Is a keto or enol normally favored?
normally the keto form is favored unless enol is stabilized by resonance or H-bonding
Enolate
anionic intermediates
places a negative charge on the alpha-carbon
Kinetic form of enol
C-C double bond is on less substituted side
Thermodynamic form of enol
C-C double bond is on more substituted side
When do we see kinetic form of enol?
at low temperatures with bulky bases
at low temperatures there is not enough energy to make the more stable product
Products of aldol condensation
aldol
or dehydration forms alpha, beta - unsaturated ketone
Aldol
aldehyde and alchohol ketone
alpha, beta - unsaturated ketone
see after aldol condensation/dehydration
C-C double bond next to a carbonyl group
LDA
strong, sterically hindered base
commonly used to make kinetic product
Michael addition
uses enolate as nucleophile and alpha, beta-unsaturated ketone to make 1,5-dicarbonyl
Robinson annulation
take 1,5-dicarbonyl from Michael addition and do another round of enolate condensation
make an enolate on the 1,5-dicarbonyl and have it attack itself
end up with six membered ring with alpha,beta-unsaturated ketone
How can we classify fructose?
fructose is a ketohexose that forms a furanose ring
What is a common triose?
glyceraldehyde
What kind of reaction forms a glycosidic bond?
dehydration
How are glycosidic bonds broken?
acid-catalyzed reactions
Sucrose
glucose and fructose
Glu(a1-B2)Fru
Maltose
2 glucose molecules
Glu(a1-4)Glu
Lactose
glucose and galactose
Glu(B1-4)Gla
Anomers
epimers that differ in orientation of their substituents at the anomeric carbon
Where is the anomeric carbon in the Fischer projection?
the anomeric carbon is the carbon in carbonyl group
Difference between hemiketal and ketal group?
hemiktal group has 1 -OH and 1 -OR
ketal group has 2 -ORs
What does nucleophilic attack on a trigonal planar substrate produce?
a mix of isomers
Millard reaction
reacts amino acids with reducing sugars
reducing sugars
act as reducing agents and become oxidized
Are monosaccharides reducing sugars?
yes, all monosaccharides are reducing sugars
How do ketoses act as reducing sugars?
keto-enol tautomerisation allows them to act as aldoses
Tollen’s test
uses Ag+ as an oxidizing agent to test for the presence of reducing sugars
Ag+ will be reduced to Ag(s) and produce silver coat
Benedict’s test
uses Cu2+ as an oxidizing agent to test for the presence of reducing sugars
Cu2+ is reduced to Cu+ which causes a color change from blue to red
How to remember Benedict versus Tollen’s test?
Benedict = BLUE
What is the relationship between glucose and galactose?
they are diasteromers at carbon 4
What is the relationship between D-glucose and L-glucose?
they are enantiomers because they differ at each stereocenter
Lowercase d/l (+/-) naming system
d is if the light is rotated to the right
l is if the light is rotated to the left
D/L naming system
look at last -OH group on Fischer projection
if it points left, L
if it points right, D
What type of amines can participate in H-bonding?
primary and secondary
Aryls
like phenyls but with NH2 instead of -OH
Are thiols capable of hydrogen bonding?
capable of very weak H-bonding
Thiols versus alcohols acidity
Thiols are more acidic because sulfurs are larger and can spread out the negative charge more that oxygens
-oate
indicates an ester
