Organic Chem Flashcards
Explain s character and bond length relation
- sp orbital = more s character = closer to nucleus = shorter and stronger bonds
- sp3 orbital = least s character = further from nucleus = longer and weaker bonds
3D representation of organic molecules
- Bonds in paper
- Dashed wedge - bonds away from observer
- Solid wedge - bond towards observer
Explain s character and electronegativity
Greater the s character = greater the electronegativity
Why are such electrons being easily available to attacking reagents
- In pi bond, parallel orientation of two p orbitals on adjacent atoms is necessary for sideways overlap
- Electron cloud of pi bond is located above and below the plane of bonding atoms
Alicyclic compounds
Carbon atoms joined in a ring (Cyclopropane, cyclohexane)
Aliphatic compounds
Straight or branched chain compounds (CH3 - CH3)
Suffix of:
1. aldehydes
2. Ketones
3. nitriles
4. Caboxylate ions
5. Esters
6. Acyl Halides
7. Amines
8. Amides
- -al
- -one
- nitrile
- oate
- -oate
- -oyl halide
- amine
- amide
Common name of:
1. Methylbenzene
2. Methoxybenzene
3. Aminobenzene
- Toulene
- Anisole
- Aniline
Structural Isomer + Example
Isomers having same molecular formula but different structures
Eg:
chain (CH3CH2CH2CH3 and CH3 - CH2 - CH3
|
CH3)
Position (CH3 - CH2 - CH2 - OH and CH3 - CH - CH3
|
OH)
Stereoisomers
Isomers that have same constition and sequence of covalent bonds but differ in relative positions of their atoms - cis and trans
Functional Isomer Example
Refers to the type of isomer where same moleculr formula but different functional groups - aldehyds and ketones for example
Explain carbocations
- Bond broken in a manner to form a carbon atom with a positive charge
- Tertiary > Secondary > Primary
- Trigonal planar shape - sp2 hybridized
Metamerism
Refers to the different alkyl chains on either side of the functional group in the molecule
C4H10O –> CH3OC3H7 and C2H5OC2H5
Carbanion
- Negative charge on carbon atom
- sp3 hybridized having distorted tetrahedron
- Primary > Secondary > Tertiary
Free radicals
- Formed by homolytic cleavage
- tertiary > secondary > primary
Substrate
A substrate refers to a molecule or compound that undergoes a chemical reaction, whether catalyzed by an enzyme, a catalyst, or an inhibito
Reagent
In chemistry, a reagent is a substance or compound added to a system to cause a chemical reaction or test if a reaction occurs.
How can electron pairs shift
- From pi bond to adjacent bond position
- From pi bond to adjacent atom
- From atom to adjacent bond position
Inductive Effect
- Polarization of sigma bond caused by the polarization of adjacent sigma bond
- Permanent effect
- More the inductive effect = More the polarity
Explain how inductive effect works
- Polarization in a way that carbon - 1 gains positive charge (since the electronegative atom pulls the electrons towards itself)
- Then carbon 2 also experiences such a pull but lesser
Electron withdrawing vs Electron donating groups
Electron withdrawing: Halogens, NO2, -CN , -COOH, COOR
Electron donating:
-CH3, -CH2 - CH3, etc.
Resonance structure
- Refers to the structure as the bonds contain an intermediate value of energy and are of different bond lengths
- In between single and double bond length
Resonance stabilization energy
Difference between the actual structure and the lowest energy resonance structure
+ and - Resonance
+ –> Transfer of electrons from an atom attached to the conjugated system
- –> Refers to the transfer of electrons towards the atom or substiuent group
Electomeric
- Temporary
- Complete transfer of a shared pair of pi electrons to one of the atoms joined by a multiple bond on the demand of an attacking reagent
- Annulled as soon as the attacking reagent is removed
Which is stronger electomeric or inductive effect?
Electomeric effect predominates
Positive vs Negative Electomeric
Hyperconjugation
- Delocalization of sigma electrons of C-H bond of an alkyl group directly attached to an atom of unsaturated system or to an atom with an unshared p orbital
- Permanent effect
Draw hyperconjugation of propene and ethene
-
Sublimation
On heating, solids changing to gaseous state directly
Crystallization
- Impure compound dissolved in a solvent where it is sparingly solublr
- Heated and concentrated to get a nearly saturated solution
- Impurities removed by adsorbing over active charcoal
Normal distillation
- Sufficient different in boiling points, hence are heated
- Vapours of lower boiling component are formed first
- Aniline and Chloroform
Fractional distillation
- Vapours of a liquid mixture are passed through a fractionating column before condensation
- Higher BP condense before as they reach up first and are more volatile
- Application: crude oil in petroleum
Distillation under reduced pressure
- Purify liquids having very high BP and decompose below BP
- They are made to boil at a temp lower than normal
- Eg: glycerol separated from spent-lye
Steam distillation
- Separate substances which are steam volatile and immiscible with water
- Mixture of steam and volatile organic compound is condensed and collected
- Atmospheric pressure = vapour pressure + water pressure
- Eg: aniline-water
Why does steam distillation have organic liquid vapourizing at a lower temp than BP
Atmospheric pressure = pressure due to organic liquid and due to water (hence since p1 lower than p, it will vaporize at a lower point)
Give examples of all distillations
- Normal: Chloroform and aniline
- Fractional: Crude oil from petroleum
- Distillation under reduced pressure: Glycerol from spent-lye in soap industry
- Steam distillation: Aniline and water
Adsorption chromatography
Different compounds are adsorbed on an adsorbent to different degrees
Commonly used adsorbents
Silica gel and alumina
Column Chromatography
- Separation of a mixture over a column of adsorbent
- Mixture adsorbed is on top of the column
- Most readily adsorbed substances are retained near the top
Thin Layer chromatography
- Separation over a thin layer of an adsorbent coated on glass plate
- Silica gel or alumina is spread over a glass plate
Partition chromatography
- Based on continuous differential partitioning of components of a mixture between stationary and mobile phases
- Solvent acts as mobile phase
Test for Nitrogen
- Na + C + N –> NaCN
- Sodium fusion extract boiled with FeSO4 and acidified with conc. H2SO4
- Prussian blue colour confirms presence of nitrogen
R value
Retardation factor = Dist. moved by substance from base line / Distance moved by solvent from base line
Detection of carbon and hydrogen
C + CuO –> Cu + CO2
H + CuO –> Cu + H2O
CO2 + Ca(OH)2 –> CaCO3 + H2O
H2O + CuSO4 –> CuSO4.5H2O
Lassaigne’s test
- Nitrogen, sulphur, halogens and phosphorus present in an organic compound are detected by Lassaigne’s test
- Elements present are converted from covalent form into ionic form by fusing compound with sodium metal
Test for sulphur
Na + S –> Na2S
* Sodium fusion extract is acidified with acetic acid and lead acetate added (Black ppt)
* Sodium fusion extract with sodium nitroprusside forms a violet colour
What happens when nitrogen and sulpur are both present
Na + C + N + S –> NaSCN
Sodium thiocynate is formed and gives blood red colour and no prussian blue
What happens when sodium fusion is carried out with excess of sodium
Thiocynate decomposes to yield cyanide and sulphide
Test for halogens
- Sodium fusion extract is acidified with nitric acid and treated with silver nitrate
white ppt soluble in NH4OH = chlorine
yellow ppt sparingly sol. in NH4OH = bromine
yellow ppt, insoluble in NH4OH = iodine
What happens for the halogen test when nitrogen or sulphur is present
- Sodium fusion extract is first boiled with conc. HNO3 to decompose cyanide or sulphide of sodium
Phosphorus test
- Compound heated with an oxidising agent (sodium peroxide)
- Solution boiled with HNO3 and treated with ammonium molybdate
- yellow ppt = phosphorus
Carbon and Hydrogen percentage
Percent C = (12 m * 100) / 44w
Percent H = (2m * 100)/18w
Dumas method
28 * (P1V1 * 273/ 760 * T) * 100 / 22400 w
Kjeldahl Method
(1.4/w * (2MV1 - MV2)
MV1 –> Molarity H2SO4, volume
MV2 –> Molarity of NaOH
When is kjeldahl’s method not applicable
Compounds containing nitrogen in nitro and azo groups and nitrogen present in the ring as nitrogen does not change to ammonium sulphate under these conditions
Carius method for halogen
atomic mass of X * m1 * 100 / molecular mass of AgX * m
Sulphur estimation
32 * m * 100 / 233 * w
Phosphorus estimations
62m * 100 / 222
Percentage oxygen estimation
32m * 100 / 88 w
Does double bond or triple bond get higher preference in naming
Double bond gets a higher preference
