Second term Flashcards
Why is it necessary to prepare sodium extract for the detection of foreign elements in organic compounds?
The preparation of sodium extract is necessary for the detection of foreign elements in organic compounds because the elements which are less commonly present in organic compound such as N,S,X,etc. are known as foreign elements are bonded through covalent bond in organic compound. Thus, do not ionize for detection, as covalent bonds are stronger. So, the foreign elements are first converted into ionic compound by fusing organic compound with sodium metal followed by chemical test for the respective elements. These sodium test for foreign elements is known as lassaigne’s test. To change elements into ionic form the organic compound must be heated with sodium extract or lassaigne’s extract.
Electrophile
Electrophiles are electron deficient, these may be positively charged or electron deficient molecules. Positively charged:- Br+, NO2+, etc. Neutral molecules:- BF3, AlCl3, FeCl3,etc.
Nucleophile
A nucleophile is a electron rich species. These may be either negatively charged or neutral molecule with lone pair of electron. Negatively charged:- X-, OH-, RO-,CN-,etc. Neutral molecule:- H2O, NH3,etc.
Free radical
A free radical is an atom or group of atoms containing odd or unpaired electron. Eg:-Cl,etc.
Inductive effect
The displacement of electron pair in covalent bond due to electronegativity difference of two joined atoms and consequently polarization of bond is called inductive effect. There are two types of inductive effect. They are negative inductive effect (-I effect) and positive inductive effect (+I effect). When an atom or group of atom carbon atom having more electronegativity, the inductive effect involved in displacement of electron away from the carbon atom is called -I effect. The group causing -I effect is called electron withdrawing group. When an atom or group of atom bonded to carbon atom having less electronegativity the inductive effect involved in the displacement of electron pair towards the carbon atom is +I effect. The group causing +I effect is called electron releasing group.
Resonance effect
The phenomenon in which molecule or ion con not be represented by a single structure rather it should be represented by more than one structure to explain its properties is called resonance effect. More than one structure of molecule or ion are called resonating structures. The hybrid of these structures are called resonating hybrid. The resonance involves delocalization of pi bond or lone pair or odd electron.
What is huckel’s rule of aromaticity
Erich Huckel, the German chemist proposed a rule for aromaticity in order to predict which compounds are aromatic. According to this rule, cyclic planar ring compound having (4n+2) (where n=1,2,3,etc.) delocalized electrons will show aromatic character i.e the aromatic compound with 2pi, 6pi, 10pi,etc will show aromatic character.
Why is -NO2 group meta directing in electrphilic aromatic substitution?
The nitro group (-NO2) attached to the aromatic ring is electron withdrawing group. It is meta directing and ring deactivator towards electrphilic substitution. This can be shown by resonance structure of nitrobenzene.
From resonating structure shown in above it is seen that in ortho and para positions, a positive charge is developed. So, meta position contains more electron density than ortho and para position. Therefore, it is easier for the incoming electrophile to attack on meta position. So, nitrobenzene undergoes electrophilic substitution on meta position.
Write short notes on orientation of electrophilic substitution in substituted benzene.
Ortho- para directing group:- The group like -NH2,-NR2,-OH,-OR,etc are ring activating groups. such groups are electron dominating group and increase electron density at ortho and para position of benzene ring. Hence these group are called ortho the para directing group.
Meta directing group:- groups like -NO2, -COR, -CHO,-CN, etc. Are ring deactivating groups. The deactivating groups deactivate the ring by the inductive effect (-I effect) in the presence of electro negative atom that withdraws the electrons away from the ring. The deactivating group directs the reaction to the meta position.
Degenerate orbitals
The electron orbitals having the same energy level are called degenerate orbitals. Px, Py, Pz are degenerate orbitals.
Rutherford nuclear model of atom
Rutherford and his co workers proceeded to perform experiments as to know where sub atomic particles were located in the atom. This experiment is known as a scattering experiment. The a particles emitted from radioactive substance where bombarded on a thin gold foil. Provided with circular zinc sulphide screen around it. When a particles strike the zinc sulphide screen a tiny flash of light was produced at a time. By examining that portion of a particles which got deflected through gold foil. From the above experiment, following observations were made:-
i. Since most a particles passed through the gold foil without deflection, it means that there is large space with the atom.
ii. Some of the a particles got deflected through small angle. It implies that there is heavy positive charge mass present at the centre of the atom which is occupying very small space. The centre of the atom named nucleus.
iii. The strong deflector or even bouncing back of particles from the gold foil due to close encounter with positively charged mass, nuclear present in atom. The nucleus is surrounded by negative charge particle which counter balance the positive charge in nucleus
Homologous series
A series of organic compound of same type in which each member differ from preceding member by constant increase of CH4 unit in their molecular formula.
Cracking
Cracking is the process whereby, complex organic molecules such as long chain hydrocarbons are broken down into simpler molecules by the action of heat.
Reforming
The process of converting aliphatic hydrocarbons containing 6 to 8 carbon atoms into aromatic hydrocarbons containing same number of carbon atoms in the presence of a catalyst like oxides of chromium, vanadium and molybdenum is called reforming or aromatization.
Aromatic hydrocarbons
Aromatic hydrocarbons are the cyclic compounds containing sigma(single bond) and delocalized pi bond or electron(double bond) between carbon atoms forming a circle.
