Organic chemistry Flashcards
2 main groups hydrocarbons are divided into
Aromatic and aliphatic
Aromatic hydrocarbons
The cyclic organic compounds which are stabilized by forming a cyclic delocalized cloud of π electrons are called aromatic compounds
simplest of aromatic hydrocarbon compounds
Benzene C6H6
Aliphatic hydrocarbons
Hydrocarbons consisting of only open carbon chains are called as acyclic aliphatic hydrocarbons while those with cyclic carbon chains are called alicyclic hydrocarbons. The aliphatic hydrocarbons are classified as alkanes, alkenes, and alkynes
Alcohols
Alcohols are compounds containing a hydroxyl group (–OH) attached to an alkyl group
An alkyl group is formally derived from an alkane by the removal of a hydrogen atom
Esters
Esters are compounds containing the COOR group
Amides
Amides are compounds containing the CONH2 group.
Ethers
Ethers are compounds containing an oxygen atom attached to two alkyl groups
Aldehydes
Aldehydes are compounds containing a carbonyl (C=O) group attached to an H atom
Ketones
Ketones are compounds containing a carbonyl (C=O) group attached to two carbon atoms each of which may belong to an alkyl or aryl group
aryl group
aryl is any functional group or substituent derived from an aromatic ring
Alkyl halides
Alkyl halides are compounds containing a halogen atom bonded to an alkyl group
Carboxylic acids
Carboxylic acids are compounds containing the carboxylic acid (COOH) group
Amines
Amines are compounds derived formally from ammonia by replacing its H atoms either by alkyl groups or aryl groups.
Lewis acids and bases
Lewis acids are compounds accepting a lone pair of electrons while Lewis bases donate a pair of electrons.
Nucleophiles and Electrophiles
chemical species that forms bonds with electrophiles by donating an electron pair. Because nucleophiles donate electrons, they are Lewis bases.
an atom or a molecule that in chemical reaction seeks an atom or molecule containing an electron pair available for bonding. Electrophilic substances are Lewis acids
Optically inactive and active compounds
Optically active compounds are compounds with chiral carbons while in optically inactive compounds chiral carbons are not found.
Priority order of functional groups
COOH, COOR, COCl, CONH2, CN, CHO, CO, OH, NH2, F, Cl, Br, I, NO2
Divisions and subdivisions of isomers of organic compounds
Constitutional isomers - chain, position and functional group
Stereoisomers - Enantiomers, Diasteromers
Stereoisomerism
Is the existence of compounds whose structures differ from each other only in the orientation of bonds in three-dimensional space.
Enantiomers
Pair of stereoisomers whose 3-dimensional structures are mirror images of each other.
compounds showing enantiomerism should contain a chiral carbon. When plane polarised light is passed through a solution containing only 1 enantiomer, the plane of polarisation rotates.
Diasteromers
Pair of stereoisomers whose 3-dimensional structures are not mirror images of each other.
Benzene ring with COOH
Benzenecarboxylic acid
Benzoic acid
Benzene ring with CH3
Toluene
Benzene ring with OH
Phenol
Benzene ring with NH2
Aniline
Benzene ring with COH
Benzenecarbaldehyde
Benzaldehyde
2 ways in which bond cleavage could occur
Heterolytic cleavage
Homolytic cleavage
Heterolytic and Homolytic cleavage
In heterolytic cleavage the 2 electrons involved in the bond will remain with 1of the atoms.
This will result in an anion and a cation.
In homolytic cleavage the 2 electrons involved in the bond will be equally divided to each atom.
This will result in 2 neutral free radicals
Free radicals
Uncharged molecules having an unpaired valency electron. They are highly reactive.
Neutral nucleophiles
NH3, H2O and SO2
Homologous series
If 2 consecutive members of a series of compounds differ only by a CH2 unit, such a series of compounds is called a homologous series.
Chain reactions
Sequence of reactions where the product of 1 reaction becomes the starting material for the subsequent reaction of the sequence.
Consist of chain initiation, propagation and termination.
Carbocations
Electron deficient positively charged trivalent carbon species
Classified as primary, secondary, tertiary and methyl
Solubility of carbocations
Tertiary > secondary > primary > methyl
Markovnikov’s rule
States that when a protic acid (HX) is added to an asymmetric alkene, the H atom is added to the carbon atom bonded to the highest number of H atoms.
Anti-Markovnikov’s rule
Hydrogen bonds are added in the opposite way when there are peroxides in the reaction medium.
In the presence of peroxides the reaction between HX and alkenes takes place via a free radical mechanism and not the ionic reaction
Halogen which does not react with alkynes
I2
Addition of H2O in the presence of Hg2+
Results in an enol (OH group) which is unstable and will rapidly convert to more stable aldehydes or ketones
Only ethynes will convert to aldehydes others will convert to ketones.
Acidic nature of alkynes with terminal hydrogen
Since a sp orbital has more s character (50% s character) than sp2 or sp3 orbitals, the bonding electrons in the C–H bond of alkynes are closer to the carbon nucleus than in the case of C–H bonds in alkenes and alkanes. Therefore the H attached to a triple bond carbon has a higher acidity than the H in alkene or alkane C–H bonds. However, the acidity of H attached to terminal alkynes is less than that of water and alcohol.
Who proposed a 6 membered ring of C atoms with alternating double and triple bond structure for benzene
Kakulé
However the structure of benzene is now considered to be a resonance hybrid of 2 kekulé structures.
resonance stabilization (or aromatic stabilization) energy of benzene
152 kJ mol-1
Characteristic reactions of benzene
Characteristic reactions of benzene are electrophilic substitution reactions and not electrophilic addition reactions as in the case of alkenes.
Arenium ion
Formation of a bond between the electrophile (E+) and a carbon atom in the benzene ring gives rise to a carbocation (arenium ion)
Acylium ion
R-C+=O
Resistance of benzene ring towards oxidation
Benzene does not get oxidized by normal oxidizing agents like KMnO4, K2Cr2O7. However, the alkyl substituted benzene can be oxidized into benzoic acid (white ppt)
Tertiary alkyl groups do not get oxidized under these conditions
Directing groups of mono substituted benzene
Ortho,para directing and activating group
Ortho,para directing and deactivating group
Meta directing and deactivating group
Ortho para directing groups
OH, R, NH2, NHR, OR
They activate the benzene ring towards electrophilic substitution by making it more electron rich than benzene
Ortho para directing and deactivating group
Cl, Br, I
Meta directing and deactivating group
NO2, CHO, COR, COOH, COOR
They deactivate the benzene ring towards electrophilic substitution by withdrawing electrons from it
Characteristics of alkyl halides
Polar compounds
Solubility in water is very low (they do not form H bonds with water)
Due the higher electronegativity of the halogen compared to the C atoms, C atom gets a slight positive charge, hence nucleophiles attack this position
Characteristic reactions of alkyl halides are nucleophilic substitution reactions
Characteristic reactions of alkyl halides are
Nucleophilic substitution reactions
Aryl halides
is an aromatic compound in which one or more hydrogen atoms, directly bonded to an aromatic ring are replaced by a halide.
Vinyl halides
In organic chemistry, a vinyl halide is a compound with the formula CH₂=CHX.
Restriction shown by aryl halides towards nucleophilic substitution reactions
Due to the resonance stabilization of the aryl halides.
Due to the resonance C-Cl bond becomes shorter and stronger compared to alkyl halides
Restriction shown by vinyl halides towards nucleophilic substitution reactions
Due to the presence of resonance which introduce partial double bond character in C-halogen bond.
Grignard reactions
Alkyl halides react with Mg in the medium of dry ether to form grignard reagent R-MgX
An electron deficient C atom is converted to electron rich C atom
Grignard reagents cannot be prepared or used in the presence of compounds which have weakly acidic H atoms including H2O
Main 2 types of alcohols
Aliphatic
Aromatic
According the no. of OH groups present alcohols are classified as
Monohydric
Dihydric
Trihydric
Polyhydric
Boiling point of alcohols
Branching of the alkyl part of the molecule leads to a reduction of boiling point
Alcohols have boiling points greater than alkanes, ethers and alkyl chlorides.
Water solubility of alcohols
Alcohols with low relative molecular masses are soluble in water
Accordingly the solubility of alcohols in water gradually decreases with increase in strength of London forces
Compounds which readily dissolve in ethanol
NaOH, Hexane
Alkoxide ion
RO-
Main 2 types of reactions of alcohols
Reactions involving cleavage of OH bond
Reaction with alkali metals and esterification
Nucleophilic substitution reactions involving cleavage of CO bond
Variation of acidic strength of terminal H of compounds
H20 > ROH > Alkynes > H2 > NH3 > RNH2
Variation of basic strength of compounds
R- > NH2- > H- > H2 > RO- > HO-
Alcohols react with carboxylic acids forming
Esters
conc.H2SO4 acts as a catalyst
Inability in reaction by breaking OH bond as primary, secondary and tertiary
Polarisation of the OH bond decreases from primary to tertiary as the electron density of the C atom connected to the OH group increases from primary to tertiary
Ability in reaction by breaking CO bond as primary, secondary and tertiary
Stability of the carbocations resulted due to the breaking of CO bond increases from primary to tertiary
Compounds tend to form stable compounds so that ability of braking the CO bond increases from primary to tertiary.
Which reaction is used to distinguish between primary, secondary and tertiary alcohols
Lucas test, Lucas reagent contains anhydrous ZnCl2 and conc. HCl
Lucas test
ZnCl2 acts as the catalyst which is an Lewis acid
ZnCl2 reacts with ROH forming alkyl halides RCl. As alkyl halides are insoluble in water (no H bonds), the solution becomes cloudy and turbid. Tertiary alcohols forms the turbidity in the shortest time as the intermediate carbocation formed is stable.
Oxidation of primary, secondary and tertiary alcohols
Undergoes oxidation with acidified K2Cr2O7, KMnO4, CrO3 and PCC (Pyridinum Chlorochromate)
Primary alcohols from carboxylic acids, However when PCC (mild oxidising agent) is used reaction is stopped at the aldehyde stage.
Secondary alcohols forms ketones (with PCC also)
Tertiary alcohols does not undergo oxidation (no H atoms)
Characteristics of phenols
Colourless crystalline solid compound
Red liquid in wet conditions
Dissolves in organic solvents
Solubility in water is very low
Non occurrence of nucleophilic substitution reactions by breaking CO bond
Due to the resonance stability of benzene ring the CO bond is shorter and stronger.
The phenyl cation formed due to the breaking of CO bond is unstable
Characteristic reaction of phenol
Electrophillic substitution reactions
Bromination of phenol
Results in white ppt of 2,4,6-tribromophenol
Br should be on oath, para positions
Acidic property of any compound depends on
Ability of releasing H+ ion
Stability of ion formed after releasing H+ ion
Stability of phenoxide ion vs phenyl cation
Stability of phenoxide ion is greater compared to the stability of phenyl cation because on phenoxide ion is there is no + charge on O atom
Acidity of phenol vs nitrophenol
NO2+ is a electron withdrawing group, Due to this OH bond in nitrophenol is more polarised than in phenol. This allows the breaking of OH bond easily releasing H+
Variation of boiling points of O containing compounds
Carboxylic acid > alcohol > ketone > aldehyde > Ether > alkane
Branching part of the alkyl group leads to reduction in boiling points
Water solubility of aldehydes and ketones
Aldehydes and ketones with relatively lower molecular masses are soluble in water
Characteristic reaction of aldehydes and ketones
Nucleophillic addition
Addition of HCN to aldehydes and ketones
Results in cyanohydrin
Reaction with Grignard reagent (aldehydes and ketones)
Results in the formation of alkoxy magnesium halide which turns to the corresponding alcohol upon hydrolysis
Ketones form tertiary alcohol
Aldehydes form secondary alcohol
Formaldehyde (HCOH) form primary alcohol
Reaction with 2,4-dinitrophenylhydrazine (2,4-DNP/ Brady reagent)
Forms 2,4-dinitrophenylhydrazone (Orange or yellow ppt)
Acidic nature of aldehydes and ketones on self condensation
H atoms attached to the carbon atoms (Alpha carbon) directly bound to the carbonyl carbon (alpha hydrogen) becomes acidic. Carbanion so formed is stabilised by resonance.
Aldehydes and ketones with alpha hydrogen undergo
Base catalysed self-condensation reactions
Reduction of aldehydes and ketones is done using
LiAlH4 (Lithium aluminium hydride) or NaBH4 (Sodium promo hydride) or Zn/Hg/conc.HCl (Clemmenson reduction)
Why LiAlH4 is used in ether medium
LiAlH4 is too reactive to be used in the presence of water or methanol
Products formed due to the reduction of aldehydes and ketones by LiAlH4 / NaBH4
Ketones give secondary alcohols
Aldehydes give primary alcohols
Methanal gives methanol
Oxidation aldehydes by Tollens reagent forms
Ag ppt (Silver mirror)
Oxidation aldehydes by Fehlings reagent forms
Blue Cu (Tartrate) turns to Cu2O (Brick red ppt)
Oxidation aldehydes by acidified KMnO4 forms
Mn2+ (pale pink)
Oxidation aldehydes by acidified K2Cr2O7 forms
Cr3+ (green)
Water solubility of carboxylic acids
Carboxylic acids with C1-C4 dissolve well in water
When the no. of carbon atom increases solubility decreases
Aromatic carboxylic acids are water insoluble
Almost all carboxylic acids soluble in organic solvents
Reduction of carboxylic acids
Undergoes reduction with LiAlH4 to form alcohols
Carboxylic acids and its derivatives do not get reduced with NaBH4 which is a less powerful reducing agent
Characteristic reactions of acid chlorides
Nucleophilic addition reaction
Reaction of acid chlorides with alcohols and phenols
Forms esters
Reaction of acid chlorides with ammonia and primary amines
With ammonia forms primary amides
With primary amines forms secondary amides
Reaction of esters with dil.mineral salts
Esters react with dilute acids and give corresponding carboxylic acid and the alcohol
Reaction of esters with NaOH(aq)
Esters when reacted with aqueous NaOH form the sodium salt of corresponding carboxylic acid and the alcohol.
Reaction of esters with Grignard reagent
Esters react with Grignard reagents to give tertiary alcohols. In this reaction, the ester is first converted to a ketone which reacts rapidly with the Grignard reagent again to give the tertiary alcohol as the product.
It is not possible to stop the reaction at the ketone stage
Reaction of esters with LiAlH4
Esters react with LiAlH4 and reduce to give alcohols.
Gives a mixture of alcohols
Reaction of amides with NaOH(aq)
When amides are warmed with an aqueous solution of NaOH, the sodium salt of the corresponding carboxylic acid is formed with liberation of gaseous NH3
Reduction of amides
Amides are reduced to the corresponding primary amine with LiAlH4
Variation of boiling points of amines
Amines have lower boiling points than alcohols
Secondary amines have less B.P than primary amines because the no.of hydrogen bonds formed in secondary amine is less
Basicity of aliphatic amines
Is more than ammonia
From primary to tertiary amines basicity increases
Reaction of amines with alkyl halides
Forms tertiary amines. Thus formed tertiary amine can react with alkyl halide further, to give a quaternary ammonium salt.
Reaction of primary amines with acid chlorides
Primary amines react with acid chlorides to give secondary amides.
Reaction of amines with nitrous acid (NaNO2/HCl)
Primary amines react with nitrous acid to form diazonium salts. As alkyl diazonium salts are unstable they rapidly convert to alcohols with the evolution of nitrogen gas.
Basicity of alcohols vs amines
amines are more basic than alcohols
Basicity aliphatic amines vs aniline
Aliphatic primary amines are more basic than aniline.
Due to the resonance stabilisation of the aromatic ring of aniline, lone pair is not readily available for a proton.
Basicity of amines vs amides
Amides are less basic than amines
It is because the pair of electrons on the nitrogen of the amide group is delocalized on to the carbonyl group by resonance
Colour of diazonium chloride
Yellow liquid
Reaction of diazonium salt with water
When aqueous solutions of diazonium salts are heated, phenols are formed.
Reaction of diazonium salt with hypophosphorus acid (H3PO2)
When diazonium salts are treated with hypophosphorous acid (H3PO2), the diazonium group is replaced by an H atom.
Reaction of diazonium salt with CuCl and CuBr
When diazonium salts are reacted with CuCl or CuBr, the corresponding aromatic halide is formed.
Reaction of diazonium salt with phenol
Benzene diazonium chloride reacts with phenol in the presence of aqueous NaOH to give an orange coloured compound, and with β-naphthol (2-naphthol) in the presence of aqueous NaOH to give a red coloured compound.
How to form an imine
RNH2 + ketone/aldehyde
In the nomenclature order which comes first, aldehydes or ketones
Aldehydes
Phenol does not react with
NaHCO3, Na2CO3
Cracking is achieved by
Sending the heavier hydrocarbons through a heated catalyst usually of zeolite (compound of aluminium, silicon and oxygen)
