NEET Chemistry syllabus is segmented into 3 parts including Organic, Inorganic, and Physical Chemistry. The chapters included in the exam are based on the question asked in class 11th and 12th. Check NEET Chemistry Syllabus
Organic Chemistry holds a weightage of 4% and different kinds of questions are asked in NEET. Some of the important chapters of Organic Chemistry include Hydrocarbons Alkanes Alkenes and Alkynes, Classification and Nomenclature, Practical and environmental chemistry, Isomerism, Haloarenes and phenols, Alcohol and ether, etc.
What is Electronegativity?
A covalent bond, where the electrons are shared equally is being referred to a nonpolar bond (eg H–H) and an unequal sharing of the pair of bonding electrons results in a polar bond. The unequal sharing of electrons is mainly because of the ability of an atom to attract electrons towards itself is referred to as Electronegativity.
Elements that have higher electronegativity values have much higher attraction for bonding electrons.
Electronegativity increase from left to right while it decreases from top to bottom.
Quick Notes on Inductive Effect
The displacement of shared pair of electrons towards the more electronegative atom within a molecule is being explained as an inductive effect. It has a permanent effect which is represented by . It develops polarity in a bond or molecule.
It is transmitted with a chain of atoms but the intensity goes on lowering the surge in the size of chain. For instance,
Therefore the transmission can be ignored after the second C-atom. An atom or group that attracts electrons strongly as compared to hydrogen will have a negative inductive effect (–I). An atom or group attracting electrons less strongly than hydrogen is said to have a positive inductive effect (+I).
Inductive effect don’t change the covalency. Better the inductive effect between a bond, the higher the ionic character of the bond would be.
What are the acid characters of acids?
Formic acid is stronger than acetic acid.
The oxygen atom in acetic acid has the hydrogen atom that is tightly after acquiring negative charge due to +I effect of methyl group. Hence it is less ionized. Acid character of halogens substituted acids. Chloro substituted acetic acids adhere to the beneath order for the acid character.
The O – H bond is much more ionic in trichloroacetic acid and its ionic character will lower from right to left. Dispersal of the negative charge after ionization will decrease from left to right that might cause decrease of acid character.
Dissociation constants (×10–5) for acids
|Acetic Acid||Monochloro acetic acid||Dichloro acetic acid||Trichloro acetic acid|
|Monofluoro acetic acid||Monochloro acetic acid||Monobromo acetic acid||Monoiodo acetic acid|
Inductive effect of halogens F > Cl > Br > I
Quick Notes on Important Topics of Organic Chemistry
Consider the inductive effect in a bond . When some negatively charged ion approaches A, the inductive effect between A – B will increase for some time. This process is being explained as an inductometric effect.
ELECTROMERIC EFFECT (E)
E includes the complete transference of p pair of electrons to one of the atoms joined a multiple bonds. It will happen for some time and happen at the requirement of attacking reagent.
The addition takes place as per Markownikoff's rule that indicates that the negative portion of attacking reagent goes to a carbon atom that has lesser hydrogen atoms. This is because the results are formed in more stable intermediate secondary carbonium ion.
What is Resonance and its applications?
Representation of some molecules by different electronic configurations is being referred to a Resonance. Electronic configurations differ only in terms of the location of electrons, the atoms will remain in the same conditions.
The real structure will be a combination of the resonance forms and this process is being referred to as Resonance hybrid.
What are some of the features of Resonance?
- Resonance is a permanent effect.
- It involves the delocalization of electrons, lone pair of electrons and p pair of electrons.
- Resonating structures that have more bonds and little charge contribute more.
- Total unpaired (not lone pairs) electrons remains the same.
- Resonating structure with lowest energy contributes more towards resonance.
- Negative charges remain more stable on electronegative atoms.
- Real structure resembles the major contributor more than the minor contributor.
- All the atoms that take part in resonance will lie in the same plane.
APPLICATIONS OF RESONANCE
ACID CHARACTER OF PHENOLS
Phenols are acidic and Alcohols are neutral.
Resonance stabilization of Phenoxide ion
Resonance stabilization of Phenol molecule
Resonance stabilisation of phenoxide ion will be more than the Resonance stabilisation of Phenol molecule. Hence Phenol will ionise to give phenoxide and H+ ions.
Basic Character Of Amines
Aromatic amines are less basic as compared to the aliphatic amines
Due to resonance the unshared pair of electrons present on the nitrogen atom is delocalised within benzene nucleus and are not present for protonation (to accept H+). Hence basic character is suppressed.
Resonance affects the Dipole moment. D.M. of ethyl chloride is 2.05 Debye.
In vinyl chloride
Inductive and resonance induced D.M. operate in opposite direction, thus it value would be 1.44 Debye.
In chlorobenzene Inductive and Resonance induced D.M. operate in opposite direction.
The value of DM is 1.55 Debye.
Some Questions with Solutions
Ques: How many σ and π bonds are present in each of the following molecules?)
HC≡CC≡CCH3 ; CH2=C=CHCH3.?
The correct answer isσ C = C : 4 (b) σ C = C : 3
σ C – H : 6 σ C – H : 6
π C = C : 3 π C = C : 2
Ques: Why are electrons easily available to the attacking reagents in π – bonds?
The electron charge cloud of the π – bond is present above and below the plane of bonding atoms. This will result in the electrons being easily available to the attacking reagents.
Ques: How are organic compounds classified?
Organic compounds are classified into three categories including:
Acyclic or open chain compounds
Alicyclic or closed chain or ring compounds.
Ques: What are homologous series?
They are being defined as the group or a series of organic compounds each containing a characteristic functional group forms a homologous series and the members of the series are called homologous.
MESOMERIC EFFECT (ME)
ME is a permanent effect and is same to electromeric effect. Like Inductive effect, it might be +ME or –ME. Positive ME atoms or groups donate electrons to the double bond or conjugated system e.g. –Cl, –Br, –I, NH2, –NHR, –NR2, –OH, –OR, –SH, –SR etc.
–ME atoms or groups withdraw electrons eg. –NO2, CN, COOH, CHO, HSO3.
The compounds that have altered single and double bonds are being referred to as conjugated compounds. These kinds of compounds exhibit some abnormal properties mainly because of interaction between single and double bonds that are referred to as conjugation
ABNORMAL ADDITION REACTIONS
Addition of HBr to 1,3-butadiene.
Each C-atom in 1, 3-butadiene is sp2 hybridised and contains one pz atomic orbital which is parallel to each other and perpendicular to the plane of hybrid atomic orbitals. By sidewise overlapping these pz atomic orbitals form a delocalised p molecular orbital that offers extra stability to the molecule.
Conjugation result in bringing changes in bond length. The C2 – C3 bond length in 1,3-butadiene is 1.47 Å and C1 – C2 bond length is 1.35Å due to conjugation.
This theory was introduced by Baker and Nathan in 1935. The electron release by C–H bond by the effect similar to electromeric effect are being referred to as hyperconjugation. It is a permanent effect.
Since there is no apparent bond between C and H+, the hyperconjugation is also being referred to as No bond Resonance. The magnitude of inductive effect and hyperconjugation follows the order mentioned below:
What will be the effect of Hyper conjugation?
The greater the number of H.C. forms the more is the stability.
Compound Heat of hydrogenation
CH2 equal to CH2 Ethylene 32.8 kcal/mol
CH3–CH equals to CH2 Propylene 30.1 kcal/mol
(Due to H.C. forms)
Tetramethyl ethylene 26.6 kcal mol.
Normal C–C = 1.54Å; C1 – C2 = 1.46Å
HYPERCONJUGATION AND DIPOLE MOMENT
The calculated dipole moment of nitro methane is 2.59 Debye while the observed value will be 3.15 Debye.
CLEAVAGE OF COVALENT BOND
Shared pair of electrons will be retained by one atom represented as:
Species that have negative charge are being referred to as anions; they are rich in electrons thus nucleophilic in nature. In a chemical reaction these kinds of species always attack at the point of low electron density. Species that have positive charge are being referred to as cations. Since they are electrons deficient therefore electrophilic in nature. In a chemical reaction they attack at the point where there is higher electron density.
HOMOLYTIC CLEAVAGE / HOMOLYSIS
The satoms retain one electron each.
The resulting species will be neutral in nature and will have at least one unpaired electron. Due to this they are referred to as free radicals, electron deficient hence electrophilic in nature, very reactive, paramagnetic in nature, hydrogen abstractor. Homolytic cleavage mostly occurs in non-polar bonds that have slightly higher temperature or under the presence of UV rays.
Some Important Questions
Ques: Name the chain isomers of C5H12 that have a tertiary hydrogen atom.
Methyl butane (CH3)2 CH – CH2 – CH3
Ques: What is heterolytic cleavage?
In heterolytic cleavage, the bond gets break in such a way further pair of electrons will remain one of the fragments.
Ques: What is carbocation?
Species that have a carbon atom possessing sextet of electrons and a positive charge is being referred to as carbocation.s
Ques: What are the nucleophiles?
The electron rich species are called mucleopiles. A nucleophile has affection for a positively charge centre. For instance, OH-, I-, CN-, : NH3, NO2-.
Some Common Definitions and Terms in Organic Chemistry
|Acid||An agent that is able to produce positively charged hydrogen ions (H+) is being referred to as Acid.|
|Achiral||A compound (or object) which is superimposible on its mirror image is being referred to as Achiral. For instance CH4.|
|Activation energy||The least energy that reacting species must possess to create an 'activated complex', or 'transition state', before proceeding to the products is being referred to a activation energy.|
|Addition reactions||Reactions where an unsaturated system gets or part saturated by the addition of a molecule across the multiple bond is known as addition reaction.|
|Allyl group:||A group that include three carbon atoms and a double bond [C1=C2-C3, where C3 is being referred to as the allyliuc position or allylic carbon atom].|
|heat of reaction||The amount of heat that is absorbed or evolved when significant amounts of compounds react under csonstant pressure. s|
|Markownikow's rule:||This rule states that in the ionic addition of hydrogen halides to a carbon-carbon double bond the halogen attaches itself to the carbon atom bearing the least number of hydrogen atoms.|
|saturated||The term given to organic molecules that have no multiple bonds.|
Important formulas of Organic Chemistry
|Name||Condensed Structural Formula||Molecular Formula|
|Butane||CH3CH2CH2CH3 or CH3(CH2)2CH3||C4H10|
Preparation tips for NEET organic chemistry
Memorize: Students must understand all the concepts and memorize all the equations, formulae, and reactions that are mentioned in the NCERT textbooks. Candidates must memorize the names of all the compounds as it is important in the exam. To get a better understanding of this section, candidates must practice different kinds of questions from reference books as well.
Focus on Inorganic Chemistry formula: Inorganic chemistry is quite an easy section of NEET Chemistry and it takes much lesser time to complete this section. Students must revise all the formulas so that basic concepts can be understood easily.
Prepare a proper strategy: Planning plays an important role while preparing for a highly competitive exam like NEET. Rather than creating a long-term goal, create small and achievable goals as it will help you monitor your progress more easily. Prepare a weekly study plan and target those topics first in which you are weak. Focus on your dream and work harder to get good results.
Refer to good books: Many times questions are asked in the NEET exam from the NCERT textbooks. Thus all the students are advised to include all the concepts taught in NCERT textbooks before moving to other reference books. Some of the reference books that can be referred include Inorganic Chemistry, J.D. Lee
Do last years’ question papers: Solving previous years’ question papers is one of the best ways to prepare for a competitive exam like NEET. Moreover doing these papers will help to ace up the preparation level and will help you get familiarity about different kinds of questions.
Previous Year Solved Sample Questions
Ques: Which among the following is the most deactivating meta-directing group in aromatic substitution reaction?
Ques: Ammonia evolved from 0.75 g of the soil sample in the Kjeldahl’s method for nitrogen estimation, neutralises 10 ml of 1M H2SO4. Find the percentage of nitrogen present in the soil
Ques: Homologous series of alkanols have a general formula
Ques: Find the compound which undergoes nucleophilic substitution reaction exclusively by an SN1 mechanism
- Benzyl chloride
- Ethyl chloride
- Isopropyl chloride
Ques: How many structural isomers are possible if one hydrogen in diphenylmethane is replaced by chlorine?