Organic Chemistry Flashcards
what is the number of covalent bonds an element forms determined by?
the number of electrons in its outer shell
what does the reactivity of a molecule derive from?
functional groups
what are the four groups of functional groups?
hydrocarbons
functional groups containing oxygen
functional groups containing nitrogen
functional groups containing sulphur
what are the different types of hydrocarbons?
alkane
alkene
alkyne
aromatic
alkyl halide
what is the general structure of alkane?
c-c
what is the general structure of alkene?
c=c
what is the general structure of alkyne?
c(triple bond) c
what is the general structure of aromatic?
benzene
what is the general structure of alkyl halide?
h3c-X
what are the different types of functional groups containing oxygen?
alcohol
ether
aldehyde
ketone
carboxylic acid
acid chloride
acid anhydride
ester
what is the general structure of alcohol?
R-OH
what is the general structure of ether?
R-OR
what is the general structure of aldehyde?
RCHO
what is the general structure of ketone?
RCOR
what are the differnt groups in the functional groupd containing nitrogen?
amine
amide
nitrile
nitro
what is the general structure of carboxylic acid?
RCO2H
what is the general structure of acid chloride?
RCOCl
what is the general structure of acid anhydride?
(RCO)2O
what is the general structure of ester?
(RCO2R)
what is the general structure of amine?
RNH2
R2NH
R3N
R4N+
what is the general structure of amide?
RCONH2
what is the general structure of nitrile?
RCN
what is the general structure of nitro?
RNO2
what are the different functional groups containing sulphur?
thiol
thioether
what is the general structure of thiol?
R-SH
what is the general structure of thioether?
R-S-R
what is functional group interconversion?
the process that allow a synthetic chemist to transform a functional group into another to change molecular properties
how does the length of the chain effect the polarity of the molecule?
longer hydrocarbon= less polar
what are the four parts of the IUPAC naming of molecules?
prefix (substituents, other functionl groups, cyclic molecule)
parent (length of main chain)
infix (unsaturation of main chain)
suffix (dominant functional group+ position if needed)
what are the steps of systematic nomenclature IUPAC?
1) identify the longest carbon chain. this becomes the parent
2) identify unsaturation. chose the infix
3) number each carbon atom in the principal chain so that the group attached to the chain has the smallest possible number
4) name the substituent. this becomes the prefix to the principal chain. decide the suffix
what is stereochemistry?
the chemistry of molecules in three dimensions
what are structural isomers?
compounds with the same olecular ormula, but atoms are bonded in different orders
what are stereoisomers?
compounds with identical molecular formulae , atoms are bonded in the same order, but in a different spatial arrangment
what are the two major types of stereoisomers?
conformational isomers
configurational isomers
what are the types of configurational isomers?
optical isomers
geometrical isomers
what needs to be present for conformational isomers?
c-c
what are chiral molecules?
cannot be superimposed on their mirroe images
what are chiral carbons?
a carbon where four difffernt groups/ atoms are present
what is an achiral carbon?
at least 2 of the same groups/atom present
what type of isomer uses chiral carbons?
configurational isomers
what are enantiomers?
same physical/ chemical properties differ in activities with plane polarised light that give rise to optical isomerism, and also in their pharmacological actions
what is a racemic mixture?
a pair of enantiomers
50;50 ratio
when a polarised light passes through there is no rotation
what are the rules applied for designating any enantiomer to R or S?
1) priotity. from 1 to 4 assigned on the basis of atomic number. higher atomic number gets higher priority
2) substituents. if no priority, the next set of atoms in the unassigned group are examined
3) double or triple bonds assigned priorities as if both atoms were duplicated or triplicated
4) arrange the molecule so that group 4 is pointing away from the viewer
what are diastereosomers?
isomers of a compound that are nonidentical and that are no -identical and not mirror images of each other
what is the equation to find out how many possible stereoisomers there are in a drug?
2^n (where n= number of chiral centres)
what are geometric isomers?
stereoisomers that arise due to the restricted rotation within a molecule
only if two different groups at each ed of double bond
what are cis/trans nomenclature isomers?
two ends of the double bond have the same group attached
both ends of the double bond have two different groups attached
but groups at the end of double bond are idential to each other
trans=identical groups on different sides
cis=identical groups are on the same side
what are E/Z nomenclature isomers?
e= higher priority groups are on different sides
z=higher priority groups are on the same side
what are nucleophiles?
love nuclei
wish to form bonds by donating or shaing electrons
are electron rich and can be negative ions, or neutral molecules with electron lone pairs
what are electrophiles?
love electrons
wish to form onds by accepting electrons or sharing electrons with a reactant molecule
are electron deficeint and can be positive ions or negative molecules
what is a double headed arrow used to show?
the movement of a pair of electrons
what is a single headed arrow used to show?
the movement of a single electron
what are the alkyl halide reactions?
nucleophilic substitution
elimination reaction
what is nucleophilic substitution?
nucleophile replaces a leaving group from a carbon atom, using its lone pair of electrons to form a new bond to the carbon atom
what is an elimination reaction?
halide ion leaves along with another atom or ion, a new pi bond results
dehydrohalogenations
reagent reacts as a base
most nucleophiles are basic and can engage in either substitution or elimination, depending on the alkyl halide and the reaction conditions
what happens in a Sn2 reaction?
nucleophile approaches electrophile from the opposite side of the molecule to the leaving group
what is a transition state?
theoretical representation of the high energy point between starting materials and products. it does not physically exist
what is Sn2?
substitution nucleophilic bimolecular reaction
what is a bimolecular reaction?
two species are involved in the rate determining step (defined as the slowest step of a reaction)
what is the transition state in Sn2?
bond to nucleophile is partially formed and the bond to the leaving group is partially broken
what are the factors affecting Sn2 reaction(nucleophile)?
Strength of nucleophiles
strong nucleophile=react faster in a Sn2 reaction
1.species with a negative charge means that there is a stronger nucleophile than a similar neutral species
2. nucleophilicity decreses from left to right , following the increase in electroneativity
3. nucleophilicity increaases down , following the increase size and polarisability
Bulkiness of the nucleophiles
bulky groups on the nucleophile hinder the close approach which slows the reaction
Solvent effect on nucleophilicity
protic solvent=reduce nucleophilicity
aprotic solvents=enhance nucleophilicity
polar aprotic solvents= enhance solubility
what is basicity?
defined by the equilibrium constant for abstracting an acidic proton; forms a new bond to a proton, it has reacted as a base
what is nucleophilicity?
defined by the rate of attack on an electrophillic carbon atom; forms a new bond to carbon, it has reacted as a nucleophile
why can electrons form bonds at relatively long distances?
electrons are more loosely held, can move freely toward a positive charge resulting in stronger bonding enhancing the atoms ability to begin to form a bond at a relatively long distance
what are protic solvents?
OH/NH groups
H-bonds to negatively charged nucleophiles
very good in solubilising reagents
what are aprotic solvents?
without OH/NH group
anions are more reactive
relatively weak solvating ability
what are polar aprotic solvents?
no OH or NH
reverse the nucleophilicity order
what are the factors affecting Sn2 reaction (substrate)?
Leaving effects on the substrate
1. electron withdrawing: polarise the carbon atom and stabalises the negative charged transition state
2. stable once has left
Steric effect on the substrate
highly dependant on the structure of the electrophile (more H present on each carbon the faster the reaction)
what is Sn1 reaction?
substitution nucleophilic unimolecular reaction
nucleophile reacts after the slow step
reaction rate does not depend on the concentration of thr nucleophile but depends only on the concentration of the substrate (electrophile)
what is a unimolecular reaction?
only one species is involved in the rate determining step
what is the process of Sn1 reaction?
step 1: formation of carbocation
step 2: nucleophilic attack on the carbocation
final step : loss of proton to solvent
what are the factors affecting Sn1 reaction (substrate)?
Substituent effect
the easier the formation of the carbocation intermediate, the faste the Sn1
the more stable the carbocation, the faster the Sn1
Resonanse stabilisation
the carbocation promotes the Sn1 reaction
Leaving group effects
weak base very stable after it leaves with the pair of electrons that bonded it to carbon
what stereochemistry is shown from Sn1 reaction?
racemisation reaction
what stereochemistry is shown from Sn2 reaction?
stereospecific reaction
what is the reason for rearrangement in Sn1 reaction?
carbocations often rearrange to form more stable carbocations
what is an elimination reaction?
loss of two atoms or groups from the substrate, usually with formation of a new pi-bond
what dehydrohalogenation?
elimination of a proton and a halide ion
resulting in an alkene
what undergoes an elimination reaction?
alkyl halides undergo eliminations to akenes
what is E1 reaction?
rate limiting transition state involves a single molecule
what are the steps in the E1 reaction?
step 1: unimolecular ionisation to give a carbocation
step 2: deprotonation b a weak base gives the alkene
what is the rder of reactivity of Sn1 and E1?
based on carbocation stability
3»2»1(no)
what are the steps in the rearrangenent in E1 reaction?
step 1: ionisation to form a carbocation
step 2: a hybride shift forms amore stable carbocation
step 3: the weakly basic solvent removes either adjacent proton
what is Zaitsev’s rule?
in elimination reactions, the most substituted alkene usually predominates
what is E2 reaction?
rate limiting transition state involves two molecules
what are the methods for synthesis of alkenes?
dehydrohalogenation of alkyl halides
dehydration of alcohols
dehydrogenation of alkanes
hofman and cope eliminations
reduction of alkynes
wittig reaction
what are the steps in alkene synthesis by dehydration of alcohols?
step 1: protonation of the hydroxy group
step 2: ionisation to a carbocation
step 3: deprotonation to give the alkene
what are alkenes reactivity?
alkene double bond is a gateway functional group
nucleophiles attack the carbocation forming a stable product: electrophilic addition
what are the steps in electrophilic addition to alkenes?
step 1: attack of the pi bond on the electrophile forms a carbocation
step 2: attack by a nucleophile gives the addition product
what is markonikovs rule?
addition of aproton acid to c=c: product with the acid proton bonded to the carbon atom that already hods the greater number of hydrogen atoms
what are the steps in the hydration of alkenes?
step 1: protonation of the double bond forms a carbocation
step 2: nucleophilic attack by water gives aprotonated alcohol
step 3: deprotonation gives the alcohol
what are the steps in the additio of halogens to alkenes?
step 1: electrophilic attack forms a halonium ion
step 2: the halide ion opens the halonium ion
what is catalytic hdrogenation of alkenes?
H2 added across the double bond to give an alkane
what is epoxidation of alkenes?
form a three-membered cyclic ether with new carbon-oxygen bonds
what is dihydoxylation of alkenes?
converting an alkene to a glycol
what is oxidative cleavage of alkenes?
stronger conditions can further oxidise glycols to cleave the bond that was originally the double bond
what is oxymercuration-demercuration of alkenes?
another method for hydrating an alkene with Markovnikov orientation
what is hydroboration-oxidation of alkenes?
method for hyf=drating an alkene with anti-Markinkov orientation
what are the ways to synthesise alkynes?
- alklation of acetylide ions
- addition of acetylide ions to carbonyl groups
3.elimination reactions
what are some reaction of alkynes (addition to the triple bond?
- reduction to alkanes
- reduction to alkenes
- addition of halogens
- addition of hydrogen halides
- addition of water
what are some reactions of alkynes (oxidation of the triple bond)?
- oxidation to alpha-dikentones
- oxidative cleavage
what are some of the features about alcohol?
organic compounds containing hydroxy groups
polar
alcohols are soluble in water
molecules with alcohol groups can H-bond to proteins
what are some of the ways to synthesise alcohols?
- nucleophilic substitution on an alkyl halide
- synthesis of alcohols from alkenes
- addition of acetylides to carbon compounds
what are organomettalic compounds?
covalent bonds between carbon atoms and metal atoms
what are the steps in using organometallic reagents for alcohol synthesis?
step 1: fromation of the gringard reagent
step 2: the gringard reagant attacks a carbonyl to form an alkoxide salt
step 3: after the first reaction is complete, water/dilute acid is added to protonate the alkoxide and give the alcohol
what are the steps for the reduction of the c=o synthesis of 1 and 2 alcohols using sodium borohydride (NaBH4)?
step 1: borohydride transfers a hydride ion to carbon, forming an alkoxide ion
step 2 : the alcohol solvent protonates the alkoxide
what are the steps for the reduction of the c=o synthesis of 1 and 2 alcohols using lithium aluminium hydride (LiAlH4)?
step 1: LAH transfers a hydride ion to carbon, forming an alkoxide ion
step 2: after the first reaction is complete, water / dilute acid is added to protonate the alkoxide
what are the differnt outcomes of oxidation of alcohols?
oxidation of primary alcohols to carboxylic acids (excess NaOCl and H2CrO4)
oxidation of primary alcohols to aldehydes (NaOCl and PCC)
oxidation of secondary alcohols to ketones (NaOCl and H2CrO4)
what are the steps in the formation of tosylates?
step 1: activation to tosylate
step 2: Sn2 displacement of tosylate ion
what are the differnt reactions for the conversion of alcohols to alkyl halides?
- reaction with hydrohalic acids
- reactions with Phosphorus halides
- reactioms with thionyl chloride
what are the steps in dehydration reactions of alcohols?
step 1: protonation of the hydroxy group
step 2: ionisation to a carbocation
step 3: deprotonation to give the alkene
what is condensation?
reaction that joins two molecules often with the loss of a small molecule such as water
what are the different synthesis of epoxides?
- peroxyacid epoxidation
- base-promoted cyclisation of halohydrins
what is esterification of alcohols?
replacing the OH- group of a carboxylic acid with the OR- group of an alcohol
what is the william ether synthesis?
alkoxide ion reacts with primary alkyl halides and tosylates to form ethers
Sn2 mechanism
if alkyl halide are hindered: elimination
what is an epoxide?
three membered cyclic ether
relatively unreactive and commonly used as solvents
what are the different ways of opening an epoxide?
- acid-catalysed
- base catalysed
in acid catalysed opening of epoxides what are the different reacters?
a. in water to form glycols
b. in alcohols to form an alkoxy alcohol
c. using hydrohalic acids
in base catalysed opening of epoxides what are the different reactors?
with alkoxides or hydroxide
with organometallics
what is an aromatic compiund?
a cyclic compound containing some number of conjugated double bonds and having an unsusually large resosnance energy
what does a resonance hybrid of the two Kekule structures show?
the pi electrons are delocalised
what criteria must aromatic compounds follow?
structure must be cyclic, containing some number of the conjugated pi bonds
each atom in the ring must have an unhybridized p otbital
unhybridized p orbitals must overlap to form a continuous ring of parallel orbitals (conugated)
delocalisation of the pi electrons over the ring must lower the electronic energy
out of the 4 criteria for aromatic compounds, which 3 do antiaromatic compounds follow?
the first three,but delocalisation pi electrons over the ring increases the electronic energy
what is a non aromatic compound?
cyclic compound that does not have continuous, overlapping ring of p orbitals. its electronic energy is similar ti that of its open-chain counterpart
what is Huckels rule?
Hückel’s Rule: If the number of pi-electrons in the cyclic system is:
(4N + 2), the system is aromatic
(4N), the system is antiaromatic
N is an integer, commonly 0, 1, 2, or 3
a cyclic compound must have a continuous ring of overlapping p orbitals, usually in a planar conformation
what are heterocyclic compunds?
rings containing sp2 hybridised heteroatoms
what are polynuclear aromatic hydrocarbons?
two or more fused benzene rings share two carbon atoms and the bond between them.
where is the ortho position?
on the next carbon
where is the para position?
on the opposite carbon
where is the meta composition?
on the second carbon attached
what is a benzyl group?
benzene ring+ methylene group
what is an aryl group?
aromatic group after the removal of a H atom from an aromatic ring. the phenyl group, Ph, is the simplest aryl group
what are the aromatic compounds reactions?
- Electrophilic aromatic substitution
- Nucleophilic aromatic substitution
- Organometallic Couplings
- Addition reactions
- Side-chain reactions
- Oxidation of phenols to quinones
what are the steps in electrophilic aromatic substitution?
step 1) attack on the electrophile forms the sigma complex
step 2) loss of a proton regains aromaticity and gives the substitution product
what are the different types of electrophilic aromatic substitution?
bromination of benzene
nitration of benzene
sulfonation of benzene
the friedel crafts alkylation
the friedel crafts acylation
whats the difference between acylation and alkylation?
alkylation forms a carbocation
acylation forms an acylium ion
what is the outcome of actiating, ortho, para-directing substituents?
primarily substitution at the ortho and para positions, methyl group is an ortho, para directing
what is inductive stabilisation?
donate electron density through the sigma
bond to the benzene ring
what is reonance stabilisation?
oxygen atom is called resonance-donating
or pi-donating because it donates
electron density through a pi bond
in one of the resonance structures
what is a deactibvating, meta-directing substituents?
deactivate the meta position less than the ortho/para positions, allowing meta substitution
what is a deactivating substituents?
groups with positive charge on the atom bonded to the aromatic ring
what are halogens in regards to benzene substitution?
deactivating groups but ortho, para-directing
what are stronger directors, activating or deactivating groups?
activating groups
what are the different ways you can do organometallic coupling?
- coupling using lithium dialkylcuprate reagents (Gilman reagents)
2.the heck reaction - the suzuki reaction (suzuki coupling)
what types of reaction can phenol have?
- fisher esterification
- williamson ether synthesis
- oxidation to quinones
what is a carbonyl group?
sp2 hybridized C connected to an O by a double bond
what are the c=o bond strengths?
C=O bond is very strong
C-O 336kJmol-1 C=O 695kJmol-1
C-C 346kJmol-1 C=C 598kJmol-1
what are the carbonyl group reactions?
1) If product stable, reaction stops here: Nucleophilic Addition to C=O
2) If R1 good leaving group: Nucleophilic Substitution to C=O (only for COOH)
3) If Nuc has lone pair- loses OH: Nucleophilic Substitution + Replacement of O
what is a ketone?
two alkyl groups bonded to the carbonyl carbon atom
what is an aldehyde?
one alkyl group and one H bonded to the carbonyl carbon atom
what does a positively polarised carbon act as?
electrophile (Lewis acid)
what does a negatively polarised oxygen act as?
nucleophile (Lewis base)
what are the ways to synthesise ketones and aldehydes?
- oxidation of alcohols
2.ozonolysis of alkenes - friedel-crafts acylation
- hydration of alkynes
- synthesis of ketones using organolithium reagents with carboxylix acids
- synthesis of ketones using organocuprates with acid chlorides
- synthesis of ketones from nitriles
- aldehyde synthesis by reduction of nitriles
- aldehyde synthesis by reduction of acid chlorides
- aldehyde syntheis by reduction of esters
what are the reactions of ketones and aldehydes?
nucleophilic addition
acid conditions with weak nucleophile and activated carbonyl
aqueous solution; ketone/aldehyde is in equilibrium with its hydrate (gemini diol)
1. addition of organometallic reagents
2. reduction
3. formation of cyanhydrins
4. formation of imines
5. conensation with hydroxylamine and hydrazine
6. formation of acetals
7. the wittig reaction
what is tautomerism?
isomerisation occuring by the migration of a proton and the movement of a double bond. the isomers that interconvert are called tautomers
what is a carboxyl group?
combination of a C=O and an -OH on the same C
what is an aliphatic acid?
alkyl group bonded to the carboxyl group
wat is an aromatic acid?
aryl group bonded to the carboxyl group
what are the synthesis of carboxylic acids?
- oxidation of primary acohols and aldehydes
- oxidative cleavage of alkenes and alkynes
- carboxylation of gringard reagents
- fromation and hydrolysis of nitriles
what are the 4 major types of reactions of carboxylic acids?
deprotonation
nucleophilic acyl substitution
reduction
decarboxylation
what is a nucleophilic acyl substitution?
one nucleophile replaces another on the acyl carbon atom
what are the reactions of carboxylic acids?
nucleophilic acyl substitution basic and acidic conditions
methods to convert carboxylic acids to esters
methods to convert carboxylic acids to amides
what is the synthesis of acid chlorides?
- reaction with alcohols to form esters
- reaction with ammonia or amines to form amides
- reaction with carboxylic acids to form anhydrides
- reduction to aldehydes
what are the carboxylic acid derivatives?
acyl halide
anhydride
ester
amide
nitril
what are the factors affecting the basicity of amines?
- Hybridisation of the Nitrogen: In heterocycles, N is sp2
hybridised. Increasing s-character brings electrons
closer to the nucleus, reducing the tendency to bond to
a proton, compared to sp3 hybridised nitrogens. - Resonance stabilisation: Lone pair shared with the ring
in aryl amines (reduced basicity) - Inductive Stabilisation: Alkyl groups donate electron to
the more electronegative N increasing the electron
density of N and making it more basic
what are the reactions of amines?
reaction of amines with ketones and aldehydes
electrophilic aromatic substitution of arylamines
alkylation of amines by alkyl halides
acylation of amines by acid chlorides
fromation of sulphonamides
hofmann elimination: amines to alkenes
oxidation of amines
cope elimination: amines to alkenes
diazotization
what are the ways for amines synthesis?
reductive amination
acylation-reduction of amines
suntheses limited to primary amines (5 diff ways)
nucleophilic aromatic substitution
amide rearrangement
