General Organic Chemistry

1. Electronic Displacements in Organic Molecules
(a) Inductive effect: Inductive effect may be defined as the permanent displacement of electrons forming a
covalent bond towards the more electronegative element or group.
The inductive effect is represented by the symbol, the arrow pointing towards the more electronegative
element or group of elements. Thus in case of n-butyl chloride inductive effect may be represented as below.
Any atom or group, if attracts electrons more strongly than hydrogen, it is said to have a -I effect (electronattracting
or electron-withdrawing), viz NO2, Cl, Br, I, F, COOH OCH3, etc. while if atom or group attracts
electrons less stronlgy than hydrogen it is said to have +I effect (electron repelling or electron-releasing) viz,
CH3, C2H5, Me2CH and Me3C groups. The important atoms or groups which cause negative or positive
inductive effect are arranged below in the order of decreasing effect.
-I (Electron-attracting) groups:
+I (Electron-attracting) groups:
(b) Resonance and Resonance (Mesomeric) effect.
Resonance: The phenomenon in which two or more structures can be written for the true structure of a
molecules, but none of them can be said to represent if uniquely, is referred to as resonacne or mesomerism.
The true structure of the molecule is said to be a resonance hybrid of the various possible alternative
structures which themselves are known as resonating structures or canonical structures. Every two adjacent
resonating structures are represented by inserting a double headed arrow between them. Thus the actual
structure of benzene may be represented in the following two ways.
Necessary conditions for resonance

1. All resonating structures must have the same arrangement of atomic nuclei.
2. The resonating structurs must have the same number of paird and unpaired electrons. However, they differ
in the way of distribution of electrons.
3. The energies of the various limiting structures must be sane or nearly the same.
4. Resonating structures must be planar.
All the resonating structures do not contribute equal to the real molecule and hence only the major
contributing forms are used while represeenting a resonance hybrid.
The mesomeric effect may be defined as the permanent effect in which p electrons are transfered from a
multiple bond to an atom, or from a multiple bond to a single covalent bond or lone pair(s) of p-electrons
from an atom to the adjacent single covalent bond.
Like inductive effect, the mesomeric effect (denoted by M) may be +M and -M. It is +M when the
transference of electron pair is away from the atom and -M when transference of electron pair is toward the
atom. In general.
Some common atoms or groups which cause +M and -M effect are given below
+M groups. -Cl, -Br, -I, -NH2, -NR2, -OH, -OCH3
- M groups. -NO2, -CN, >C=O
(c) Electromeric effect: This type of temporary displacement of electrons take place in compounds
containing multiple covalent bonds (e.g. C=C, C=O, C°N, etc.) or an atom with a lone pair of electrons
adjacent to a covalent bond. The effect involves complete transference of a pair of electrons from a multiple
bond to an atom, or from a multiple bond to another bond, or from an atom with a free pair of electrons to a
bond. it is the p-electrons of a multiple bond, or the p-electrons of an atom, which are transfered. Since the
effect involes complete transference of electrons, it leads to the development of full + and - charges within
the molecule. It is important to note that the electromeric effect is purely a temporary effect and is brought
into play only the requirement of attacking reagent, it vanishes out as soon as the attacking reagent is
removed from reaction mixture.


for more details please visit: http://www.gurukpo.com/

Aldol Condensation

In some cases, the adducts obtained from the Aldol Addition can easily be converted (in situ) to α,β-unsaturated carbonyl compounds, either thermally or under acidic or basic catalysis. The formation of the conjugated system is the driving force for this spontaneous dehydration. Under a variety of protocols, the condensation product can be obtained directly without isolation of the aldol.

---

Mechanism of the Aldol Condensation

for more details please visit:- http://www.gurukpo.com/

resonence

RESONANCE OR MESOMERISM IN ORGANIC CHEMISTRY

 Sometimes, it is not possible to represent the molecule or ion with only one structure. More than one structure have to be proposed. But none of them explains all the observed properties of the molecule. The solution is to write a weighted average of all the valid structures, which explains all the properties. This condition is usually referred to as resonance or mesomerism or delocalization.
The representation of structure of a molecule as a weighted average of two or more hypothetical structures, which only differ by the arrangement of electrons but with same positions for atoms is referred to as resonance.
Salient features of resonance: 
* The hypothetical structures with different arrangement of electrons but with identical positions for atoms are called resonance structures or canonical forms or contributing structures. 
* The resonance structures are only imaginary and the actual structure of the molecule is considered as the hybrid of all the valid resonance structures.
Resonance hybrid: The weighted average of contributing structures is known as resonance hybrid. It is considered as the actual structure.
* The energy of resonance hybrid is always less than the energy of any of the contributing resonance structure. 
* The resonance structures are formed (only on paper!?) due to delocalization of electrons and not by changing the positions of atoms.
* The delocalization of electrons is shown using curved arrows.
One should keep in mind that the individual resonance structures do not exist and the molecule do not resonate (switch back and forth) between these structures. The actual molecule is simply the hybrid of all these imaginary resonance structures. Hence the delocalization of electrons is also imaginary process which helps in understanding the resonance.
Illustration: 
From the following structure (I) - representing urea, 

it is expected that: 

1) It should be a diacidic base, 

2) The bond length of C-N bond is equal to the normal C-N bond length and

3) No dipole moment since it is symmetrical. 

However it is observed that: 

1) Urea is a monoacidic base,

2) It has shorter than expected bond length for C-N bond and

3) It shows dipole moment. 

Hence, to account for above observations,  the actual structure of urea is represented as a resonance hybrid of following resonance structures. 

Note: The contributing structures are always shown to be linked by using double headed arrows ().
 

RULES THAT HELP IN WRITING VALID RESONANCE STRUCTURES

The valid resonance structures must satisfy the following rules: 
* They must be valid Lewis structures obeying octet rule. 
E.g. Carbon or Nitrogen with five bonds is not allowed.
In the structure (II), the nitrogen atom violated the octet. It has 10 electrons around it.

 

* They should possess same number of electrons and equal net charge.
* The number of unpaired electrons in them must be same. 
E.g. Following structure for butadiene is not valid. 

* The positions of atoms should be same in all the resonance structures.
E.g. The following are not the resonance structures, since the position of one hydrogen atom is not same. Indeed, they are different molecules, which are in dynamic equilibrium with each other. These are called tautomers. Also note that these molecules are linked by two half headed arrows and not by a single double headed arrow.

 

* The bond order of two connecting atoms may vary between two different resonance structures. 
* The resonance structures may or may not be equivalent. 
* The atoms that are part of the delocalized system must be arranged in one plane or nearly so. The reason is to get maximum overlap between the orbitals.
 

STABILITY OF RESONANCE STRUCTURES 

* The actual structure i.e., resonance hybrid of a molecule has lower energy than any of the contributing form and hence the resonance is a stabilizing phenomenon.
* Greater the number of contributing structures, greater is the stability of the resonance hybrid. 
* All the structures do not contribute equally to the hybrid. 
* Greater the stability of a resonance structure, larger is its contribution to the resonance hybrid.
 
Rules to decide the major contributor to the hybrid in the decreasing order of preference are given below: 
* The contributing structures that have atoms with full octets are more stable than the ones with open octets. 
* The contributing structure with more covalent bonds is more stable. 
E.g. Among the following, the structure II is more stable since all the atoms have octet configuration and there are more covalent bonds.

* Resonance structures with fewer charges are more stable than those with more charges.
E.g. The second structure with two negative charges is not only less stable.

* The structure with less charge separation is more stable. 
E.g. Among the following resonance forms of phenol, the structure I is more stable since it has no charge. Whereas the structures II and IV have less charge separation and are more stable than the structure III.

* The structure with charge dispersal or delocalization over more number of atoms is more stable. 
* The structures in which the atoms bearing the conventional charges are more stable i.e., the more electronegative atom should bear negative charge while the relatively less electronegative atom should bear positive charge. 
E.g.

 
Resonance stabilization energy: The difference between the energy of resonance hybrid and that of most stable resonance structure of a molecule is known as the resonance stabilization energy of that molecule.
 

EXAMPLES OF RESONANCE STRUCTURES

1) The following resonance structures can be written for benzene which are hypothetically possible due to delocalization of π electrons. The Kekule structures have more weightage than Dewar structures. 

 

The actual structure of benzene is thus shown to be the hybrid of these contributing structures. The bond order of every C-C bond is 1.5 and hence the every C-C bond length is reported to be same and equals to 1.39 A^o, which is in between the bond length values of C-C single bond (1.54 A^o) and C=C double bond (1.20 A^o).
Due to resonance, benzene gets extra stability and does not undergo electrophilic addition reactions. However it shows electrophilic substitution reactions. This phenomenon is known as aromaticity.

for more details please visit:- http://www.gurukpo.com/

 INDUCTIVE EFFECT :-

The C-Cl bond in the butyl chloride, CH₃-CH₂-CH₂-CH₂-Cl is polarized due to electronegativity difference. The electrons are withdrawn by the chlorine atom. Thus the first carbon atom gets partial positive charge. In turn, this carbon atom drags electron density partially from the next carbon, which also gets partial positive charge. Thus the inductive effect is transmitted through the carbon chain. 

But the inductive effect weakens away along the chain and is not significant beyond 3rd carbon atom.

TYPES OF INDUCTIVE EFFECT

The inductive effect is divided into two types depending on their strength of electron withdrawing or electron releasing nature with respect to hydrogen. 
1) Negative inductive effect (-I): The electron withdrawing nature of groups or atoms is called as negative inductive effect. It is indicated by -I. Following are the examples of groups in the decreasing order of their -I effect: 
NH₃⁺ > NO₂ > CN > SO₃H > CHO > CO > COOH > COCl > CONH₂ > F > Cl > Br > I > OH > OR > NH₂ > C₆H₅ > H 
 
2) Positive inductive effect (+I): It refers to the electron releasing nature of the groups or atoms and is denoted by +I. Following are the examples of groups in the decreasing order of their +I effect. 
C(CH₃)₃ > CH(CH₃)₂ > CH₂CH₃ > CH₃ > H
Why alkyl groups are showing positive inductive effect?
Though the C-H bond is practically considered as non-polar, there is partial positive charge on hydrogen atom and partial negative charge on carbon atom. Therefore each hydrogen atom acts as electron donating group. This in turn makes an alkyl group, an electron donating group.

 

APPLICATIONS OF INDUCTIVE EFFECT

Stability of carbonium ions: 
The stability of carbonium ions increases with increase in number of alkyl groups due to their +I effect. The alkyl groups release electrons to carbon, bearing positive charge and thus stabilizes the ion. 
The order of stability of carbonium ions is : 

Stability of free radicals: 
In the same way the stability of free radicals increases with increase in the number of alkyl groups. 
Thus the stability of different free radicals is:

Stability of carbanions: 
However the stability of carbanions decreases with increase in the number of alkyl groups since the electron donating alkyl groups destabilize the carbanions by increasing the electron density. 
Thus the order of stability of carbanions is:
 
Acidic strength of carboxylic acids and phenols: 
The electron withdrawing groups (-I) decrease the negative charge on the carboxylate ion and thus by stabilizing it. Hence the acidic strength increases when -I groups are present. 
However the +I groups decrease the acidic strength. 
E.g. 
i) The acidic strength increases with increase in the number of electron withdrawing Fluorine atoms as shown below. 
CH₃COOH < CH₂FCOOH < CHF₂COOH < CF₃COOH 
ii) Formic acid is stronger acid than acetic acid since the –CH₃ group destabilizes the carboxylate ion. 
On the same lines, the acidic strength of phenols increases when -I groups are present on the ring. 
E.g. The p-nitrophenol is stronger acid than phenol since the -NO₂ group is a -I group and withdraws electron density. Whereas the para-cresol is weaker acid than phenol since the -CH₃ group shows positive (+I) inductive effect. 
Therefore the decreasing order of acidic strength is:

Basic strength of amines: 
The electron donating groups like alkyl groups increase the basic strength of amines whereas the electron withdrawing groups like aryl groups decrease the basic nature. Therefore alkyl amines are stronger Lewi bases than ammonia, whereas aryl amines are weaker than ammonia. 
Thus the order of basic strength of alkyl and aryl amines with respect to ammonia is :CH₃NH₂ > NH₃ > C₆H₅NH₂ 

Reactivity of carbonyl compounds:
The +I groups increase the electron density at carbonyl carbon. Hence their reactivity towards nucleophiles decreases. Thus formaldehyde is more reactive than acetaldehyde and acetone towards nucleophilic addition reactions. 
Thus the order of reactivity follows:

 

for more details please visit:- http://www.gurukpo.com/

confermational analysis

Conformational analysis of ethane

A conformational analysis is a study of the energetics of different spatial arrangements of atoms relative to rotations about bonds. Conformational analyses are assisted greatly by a representation of molecules in a manner different to skeletal structures. A representation of a molecule in which the atoms and bonds are viewed along the axix about which rotation occurs is called a Newman projection (Figure 1).

Figure 1: Newman projection of ethane
In a Newman projection, the molecule is viewed along an axis containing two atoms bonded to each other and the bond between them, about which the molecule can rotate. In a Newman projection, the "substituents" of each atom composing the bond, be they hydrogens or functional groups, can then be viewed both in front of and behind the carbon-carbon bond. Specifically, one can observe the angle between a substituent on the front atom and a substituent on the back atom in the Newman projection, which is called the dihedral angle or torsion angle.
In ethane specifically, we can imagine two possible "extreme" conformations. In one case, the dihedral angle is 0° and the hydrogens on the first carbon line up with or eclipse the hydrogens on the second carbon. When the dihedral angle is 0° and the hydrogens line up perfectly, ethane has adopted the eclipsed conformation (Figure 2). The other extreme occurs when the hydrogens on the first carbon are as far away as possible from those on the second carbon; this occurs at a dihedral angle of 60° and is called the staggered conformation (Figure 2).

Figure 2: Conformations of ethane - staggered and eclipsed
The staggered conformation of ethane is a more stable, lower energy conformation than the eclipsed conformation because the eclipsed conformation involves unfavorable interactions between hydrogen atoms. Specifically, the negatively charged electrons in the bonds repel each other most when the bonds line up. Thus, ethane spends most of its time in the more stable staggered conformation.

Conformational analysis of butane

In butane, two of the substituents, one on each carbon atom being viewed, is a methyl group. Methyl groups are much larger than hydrogen atoms. Thus, when eclipsed conformations occur in butane, the interactions are especially unfavorable. There are four possible "extreme" conformations of butane: 1) Fully eclipsed, when the methyl groups eclipse each other; 2) Gauche, when the methyl groups are staggered but next to each other; 3) Eclipsed, when the methyl groups eclipse hydrogen atoms; and 4) Anti, when the methyl groups are staggered and as far away from each other as possible (Figure 3).

Figure 3: Conformations of butane: fully eclipsed, gauche, eclipsed, and anti
The fully eclipsed conformation is clearly the highest in energy and least favorable since the largest groups are interacting directly with each other. As the molecule rotates, it adopts the relatively stable gauche conformation. As it continues to rotate, it encounters less favorable eclipsed conformation in which a methyl group eclipses a hydrogen. As rotation continues, the molecule comes to the anti conformation, which is the most stable since the substituents are staggered and the methyl groups are as far away from each other as possible. An energy diagram is a graph which represents the energy of a molecule as a function of some changing parameter. An energy diagram can be made as a function of dihedral angle for butane (Figure 4).

Figure 4: Energy diagram for conformations of butane as a function of dihedral angle
Clearly, the anti and gauche conformations are significantly more stable than the eclipsed and fully eclipsed conformations. Butane spends most of its time in the anti and gauche conformations.
There is one final, very important point. At room temperature, approximately 84 kJ/mol of thermal energy is available to molecules. Thus, if the barrier to a rotation is less than 84 kJ/mol, the molecule will rotate. In ethane and butane, the barriers to rotation are significantly less than 84 kJ/mol. Therefore, even though the eclipsed conformations are unfavorable, the molecules are able to adopt them. In reality, since these conformations are not as stable, the molecules will quickly pass through them at room temperature and return a staggered conformation. Molecules are constantly converting between different staggered conformations all the time, quickly passing through eclipsed conformations in between. Thus, in alkanes, no single "true" conformation exists all the time; the molecule instead constantly converts between conformations, spending more time in those that are more stable. This constant conversion lies in stark contract to alkenes, which adopt the cis- or trans- (E- or Z-) conformations and retain them at room temperature; they do not interconvert because the barrier to rotation is too high.

For more details please visit:- http://www.gurukpo.com/

deepawali

happy deepawali to all of you

for more details please visit:- http://www.%20gurukpo.com/

Isomers

Bhopal disaster

Bhopal disaster

                for more details please visit:- http://www.gurukpo.com/

 Methyl isocyanate is also manufactured from N-methylformamide and air. In the latter process, it is immediately consumed in a closed-loop process to make methomyl.^[9] Other manufacturing methods have been reported

 

OPTICAL ISOMERISM

Chiral and achiral molecules
The essential difference between the two examples we've looked at lies in the symmetry of the molecules.

If there are two groups the same attached to the central carbon atom, the molecule has a plane of symmetry. If you imagine slicing through the molecule, the left-hand side is an exact reflection of the right-hand side.
Where there are four groups attached, there is no symmetry anywhere in the molecule.

A molecule which has no plane of symmetry is described as chiral. The carbon atom with the four different groups attached which causes this lack of symmetry is described as a chiral centre or as an asymmetric carbon atom.
The molecule on the left above (with a plane of symmetry) is described as achiral.
Only chiral molecules have optical isomers.

The relationship between the enantiomers
One of the enantiomers is simply a non-superimposable mirror image of the other one.
In other words, if one isomer looked in a mirror, what it would see is the other one. The two isomers (the original one and its mirror image) have a different spatial arrangement, and so can't be superimposed on each other.

If an achiral molecule (one with a plane of symmetry) looked in a mirror, you would always find that by rotating the image in space, you could make the two look identical. It would be possible to superimpose the original molecule and its mirror image.

 For more details please visit http://www.gurukpo.com/

GEOMETRICAL ISOMERISM

Geometric (cis / trans) isomerismHow geometric isomers arise These isomers occur where you have restricted rotation somewhere in a molecule. At an introductory level in organic chemistry, examples usually just involve the carbon-carbon double bond - and that's what this page will concentrate on. Think about what happens in molecules where there is unrestricted rotation about carbon bonds - in other words where the carbon-carbon bonds are all single. The next diagram shows two possible configurations of 1,2-dichloroethane. These two models represent exactly the same molecule. You can get from one to the other just by twisting around the carbon-carbon single bond. These molecules are not isomers. If you draw a structural formula instead of using models, you have to bear in mind the possibility of this free rotation about single bonds. You must accept that these two structures represent the same molecule: But what happens if you have a carbon-carbon double bond - as in 1,2-dichloroethene? These two molecules aren't the same. The carbon-carbon double bond won't rotate and so you would have to take the models to pieces in order to convert one structure into the other one. That is a simple test for isomers. If you have to take a model to pieces to convert it into another one, then you've got isomers. If you merely have to twist it a bit, then you haven't!

prostaglandins

Prostaglandin 

in mammals, a hormone that has a broad spectrum of physiological action. Prostaglandins were discovered in human semen by the Swedish scientist U. Euler in 1936. Initially, they were thought to be secretions of the prostate gland (hence the name). They were obtained in a pure form in 1956–65 by Swedish and American scientists.
About 20 natural prostaglandins are known, including thick liquids and low-melting crystalline substances. All prostaglandins are unsaturated hydroxy fatty acids that have a skeleton of 20 carbon atoms. According to their chemical structure, prostaglandins are divided into four groups—A, B, E, and F—E and F prostaglandins being the most important biologically. The subscripts in the formula below indicate the number of double bonds in the lateral chains of the molecule.

Prostaglandins are found in low concentrations (about 1 μg/g) in almost all organs, tissues, and biological fluids of higher animals. The most important physiological effect that is stimulated by prostaglandins is the ability to contract smooth muscles, especially the muscles of the uterus and fallopian tubes; at childbirth and during menstruation, the concentration of prostaglandins in uterine tissues increases substantially. For this reason, they are used in obstetrics and gynecology to facilitate normal labor and to artificially terminate pregnancy in its early stage.
Prostaglandins are also cardiotonics and bronchodilators. Arterial pressure is lowered by A and E prostaglandins and raised by F prostaglandin. A, E, and F prostaglandins intensify coronary and renal blood flow, inhibit gastric secretion, and affect the endocrine glands, including the thyroid gland; they also affect water-salt metabolism by altering the ratio Na⁺: K⁺ and blood coagulation by inhibiting the aggregation of thrombocytes.
The biosynthesis of prostaglandins occurs in the cells of different tissues. The precursors of prostaglandins are phospholipids; polyunsaturated fatty acids with a linear chain of 20 carbon atoms are released from phospholipids by the enzyme phospholipase. The oxidative cyclization of the carbon atoms, which occurs with the participation of prostaglandin synthetases (a special system of enzymes), results in the synthesis of E and F prostaglandins.
The classification of prostaglandins as local, or cellular, hormones is justified by their varied functions and the absence of a special organ for their biosynthesis. Their mechanism of action is still unclear. It has been established that prostaglandins affect the activity of the enzyme adenyl cyclase, which regulates the concentration of cyclic adenosine 3’: 5’-monophosphate (cyclic AMP) in the cell. Since prostaglandins influence the biosynthesis of cyclic AMP and since cyclic AMP participates in hormonal regulation, a possible mechanism of action of prostaglandins could consist in correcting (intensifying or weakening) the action of other hormones.

Clinical tests have shown prostaglandins to be promising in the treatment of such conditions as gastric ulcer, asthma, hypertonia, thromboses, arthritides, and inflammations of the nasopharynx. For medical and research purposes, prostaglandins are produced: (1) by enzymatic synthesis based on polyunsaturated fatty acids that are produced in the food-processing industry, (2) by complete chemical synthesis in nine to 13 stages chiefly based on cyclopentadiene, and (3) by partial synthesis in three to five stages based on prostaglandin A₂ and E₂ derivatives that are present in high concentrations (reaching 1.4 percent of the raw mass) in several varieties of the soft marine coral Plexaura homomalla.

for more details please visit:-  http://www.gurukpo.com/

SUBSTITUTION, ADDITION, AND ELIMINATION REACTIONS

Introduction:

Substitution, addition, and elimination reactions are of great importance in a major branch of chemistry known as Organic Chemistry, which covers the chemistry of compounds of carbon. These reactions, which generally involve covalently bonded molecules, are also found, to a much more limited extent with other compounds.

Substitution reactions:

A substitution reaction is a reaction in which an atom (or group of atoms) in a molecule is replaced by another atom or group of atoms:

Example 1:

The gas ethane, CH₃CH₃ reacts with bromine vapour in the presence of light to form bromoethane, CH₃CH₂Br and hydrogen bromide, HBr. In the process, a hydrogen atom in ethane has been substituted for a bromine atom:

                          

Example 2:

Ethanol, CH₃CH₂OH, reacts with hydrogen iodide, HI, to form iodoethane and water. Here, a group of atoms, OH, has been replaced by an iodine atom:

Example 3:

Benzene, C₆H₆, reacts with bromine in the (presence of iron bromide as catalyst) to form bromobenzene, C₆H₅Br. This results in a hydrogen atom being replaced by a bromine atom:

Addition reactions:

An addition reaction is a reaction whereby a molecule reacts with another molecule having one or more multiple covalent bonds so as to form a molecule whose molecular mass is the sum of the molecular masses of the reacting molecules:

Example 3:

Ethene, CH₂=CH₂ has a double bond joining the two carbon atoms. This substance can add a hydrogen molecule (in the presence of platinum as catalyst) to form ethane, CH₃CH₃:

Example 5:

Ethyne, C₂H₂ has a triple bond joining the two carbon atoms. Hydrogen bromide adds onto this triple bond to form 1,1-dibromoethane, CH₃CHBr₂:

Elimination reactions:

An elimination reaction is a reaction whereby a multiple covalent bond is formed in a molecule by the removal of another, usually smaller molecule:

Example 6:

Ethanol, CH₃CH₂OH, when treated with concentrated sulphuric acid, H₂SO₄, loses 2 hydrogen atoms and one oxygen atom, forming ethene, CH₂=CH₂ and water (the atoms that have been eliminated are shown in red):

When an elimination reaction removes the elements of water from a compound, as in the reaction above, the reaction is called a DEHYDRATION REACTION.

Example 7:

Bromoethene, CH₂=CHBr, when treated with potassium hydroxide dissolved in ethanol, loses one hydrogen atom and one bromine atom, forming ethyne, CH≡CH (the atoms that have been eliminated are shown in red):

When an elimination reaction removes the elements of a halogen acid (HCl, HBr, HI) from a compound, as in the reaction above, the reaction is called a DEHYDROHALOGENATION REACTION

for more details please visit: http://www.gurukpo.com/

Hyperconjuction

Definition of hyperconjugation

In the formalism that separates bonds into  and  types, hyperconjugation is the interaction of -bonds (e.g. C-H, C-C, etc.) with a  network. This interaction is customarily illustrated by contributing structures, e.g. for toluene (below), sometimes said to be an example of "heterovalent" or "sacrificial hyperconjugation", so named because the contributing structure contains one two-electron bond less than the normal Lewis formula for toluene


At present, there is no evidence for sacrificial hyperconjugation in neutral hydrocarbons.
The concept of hyperconjugation is also applied to carbenium ions and radicals, where the interaction is now between -bonds and an unfilled or partially filled  or p-orbital. A contributing structure illustrating this for the tert-butyl cation is:


This latter example is sometimes called an example of "isovalent hyperconjugation" (the contributing structure containing the same number of two-electron bonds as the normal Lewis formula).
Both structures shown on the right hand side are also examples of "double bond- no-bond resonance".
The interaction between filled  or p orbitals and adjacent antibonding * orbitals is referred to as "negative hyperconjugation", as for example in the fluoroethyl anion:


for more details please visit www.gurukpo.com

Hydrogen Bonding

Diffinition: When hydrogen atom connet with more electronegetive atom through covelant bond at one side and connect to  more electronegative atom at another side with week electrostatic bond, this week electrostatic bond is known as Hydrogen bond.and the process is known as Hydrogen bonding.

For more details please visit: http://www.gurukpo.com/

Thought

Be happy always!!