IIT JEE , AIEEE Forum - Fun Zone , Lounge

kghedriu

hi goiitians...........to b frank..m also a new one here...joined only one and half month ago...on Feb-7

m celebrating my 1200 altitude with all of u...

thanx all of u for ur cooperation.....i thank all the 8200 users of this site and admin sir for creating such a wonderful world for us..

all the best for all ur competitive exams.....

with best wishes.......

K.Goutham Harsha

karthik_abiram

u deserve it dude,

keep rocking...........

kghedriu

i m presenting the following information as a result of this achievement......

Formal charges

Calculating the formal charge on an atom in a molecule is a fairly simple task. After some time, calculating formal charges should become second nature and you should be able to assign formal charges on atoms very rapidly. To calculate the formal charge on an atom, you use the following equation:

formal charge = group number - non-bonding electrons -( 0.5 x shared electrons)

EXAMPLE:: Assign a formal charge to the nitrogen in the compound shown below

To calculate the formal charge on nitrogen there are three pieces of information that you need to know: the group number (number of valence electrons), the number of non-bonding electrons, and the number of shared electrons.

Nitrogen is in group five; thus, it has five valence electrons
Number of non-bonding electrons: there are no non-bonding electrons, so this is zero
Number of shared electrons: there are four bonds, and there are two electrons in each bond, so this number is eight

formal charge = 5 - 0 - 0.5(8) = +1
Thus, the nitrogen has a formal charge of +1

Electronegativity guide

Some atoms have more affinity for electrons than do other atoms, and this affinity is based upon the size of the atom and the distance of its valence electrons from its positvely charged nucleus. The measure of an atom's electron affinity is called it's electronegativity. Some atoms are highly electronegative and steal electrons from any atom it bonds to; other atoms donate electrons to any atom that it bonds to.

As a general rule of thumb, as you go up and to the right of the periodic table, the electronegativity of an atom increases. Thus, as you go up and to the right on the periodic table, you reach the bully elements such as fluorine, oxygen, and nitrogen who like to hog electrons in a bond (fluorine, at the top right, is the most electronegative element). As you go down and to the left, you reach the 98-pound weakling elements such as the metals and silicon (and carbon, to some extent)

In the illustration below, carbon atoms are shown as "weaker" than fluorine atoms at holding onto the bonding electrons (important note: "atoms" not drawn to scale. Fluorine, despite being heavier, is actually smaller than carbon, although is much more of an electron pig).

Electron hogs such as fluorine selfishly steal electron density from less electronegative atoms like carbon, creating a bond dipole

Using electronegativities

If there is a difference in electronegativity between two bonding atoms (a carbon bonded to fluorine for example), you get a separation of charge, or a dipole moment. In the C-F bond example, carbon has some of its electron density stolen from it by the highly electronegative fluorine atom and becomes partially positive charged, while fluorine, having stolen the electron density, becomes partially negative charged. You can use the dipole vector (shown below) to indicate the direction of the dipole moment in a bond, with the head pointing towards the direction of negative charge.

It is very important to understand how electronegative atoms attached to carbons form dipoles, as it is essential in the understanding of the reactivity of organic molecules. It's a good idea to look at many different bonds and predict the dipole moment of the bond using the dipole vector.

Aatish

great work khedriu !!!

BEST OF LUCK FOR THE FUTURE

diksha_jeena

congratz!!!!!!!!!!!

kghedriu

Organic Chemistry Glossary

achiral: A molecule that's superimposable on its mir ror image. Achiral molecules do not rotate plane-polarized light.

acid: A proton donor or an electron pair acceptor.

alcohol: A molecule containing a hydroxyl (OH) group. Also a functional group.

aldehyde: A molecule containing a terminal carbonyl (CHO) group. Also a functional group.

alkane:A molecule containing only C-H and C-C single bonds.

alkene:A molecule containing one or more carbon-carbon double bonds. Also a functional group.

alkyne:A molecule containing one or more carbon-carbon triple bonds. Also a functional group.

allylic carbon: An sp³ carbon adjacent to a double bond.

amide: A molecule containing a carbonyl group attached to a nitrogen (-CONR₂). Also a functional group.

amine: A molecule containing an isolated nitrogen = (NR₃). Also a functional group.

anion: A negatively charged atom or molecule.

anti addition: A reaction in which th= e two groups of a reagent X-Y add on opposite faces of a carbon-carbon bond.

anti conformation: A type of staggered conformation in which the two big groups are opposite of each other in a Newman projection.

anti-aromatic: A highly unstable planar ring system with 4n pi electrons.

anti-periplanar (a.k.a. anticoplanar): The conformation in which a hydrogen and a leaving group are in the same plane and on opposite sides of a carbon-carbon single bond. The conformation required for E2 elimination.

aprotic solvents: Solvents that do not contain O-H or N-H bonds.

aromatic: A planar ring system that contains uninterrupted p orbitals around the ring and a total of 4n+2 pi electrons. Aromatic compounds are unusually stable compounds.

aryl: An aromatic group as a substituent.

axial bond: A bond perpendicular to the equator of the ring (up or down), typically in a chair cyclohexane.

base: A proton acceptor or an electron pair donor.

benzyl group: A benzene ring plus a methylene (CH₂) unit (C₆H5?CH₂).

benzylic position: The position of a carbon attached to a benzene ring.

benzyne: A highly reactive intermediate. A benzene ring with a triple bond.

bicyclic: A molecule with two rings that share at least two carbons.

Brønsted acid: A proton donor.

Brønsted base: A proton acceptor.

carbanion: A negatively charged carbon atom.

carbene: A reactive intermediate, characterized by a neutral, electron-deficient carbon center with two substituents (R₂C:).

carbocation: A positively charged carbon.

carbonyl group: A carbon double bonded to oxygen (C=O).

carboxylic acid:A molecule containing a carboxyl (COOH) group.Also a functional group.

cation: A positively charged molecule or atom.

chair conformation: Typically, the most stable cyclohexane conformation. Looks like a chair.

chemical shift: The location of an NMR peak relative to the standard tetramethylsilane (TMS), given in units of parts per million (ppm).

chiral center: A carbon or other atom with four nonidentical substituents.

chiral molecule: A molecule that's not superimposable on its mirror image. Chiral molecules rotate plane-polarized light.

cis: Two identical substituents on the same side of a double bond or ring.

configuration: The three-dimensional orientation of atoms around a chiral center. It?s given the designation R or S.

conformation: The instantaneous spatial arrangements of atoms. Conformations can change by rotation around single bonds.

conjugate acid: The acid that results from protonation of a base.

conjugate base: The base that results from the deprotonation of an acid.

conjugated double bonds: Double bonds separated by one carbon-carbon single bond. Alternating double bonds.

constitutional isomers: Molecules with the same molecular formula but with atoms attached in different ways.

coupling protons: Protons that interact with each other and split the NMR peak into a certain number of lines following the n+1 rule.

coupling constant: The distance between two neighboring lines in an NMR peak (given in units of Hz).

covalent bond: Bond in which the two electrons are shared between the two atoms.

dehydrohalogenation: Loss of a hydrohalic acid (like HBr, HCl, and so on) to form a double bond.

delta value (a.k.a. d value): The chemical shift. The location of an NMR peak relative to the standard tetramethylsilane (TMS), given in units of parts per million (ppm).

diastereomers: Stereoisomers that are not mirror images of each other.

Diels-Alder reaction: A reaction that brings together a diene and a dienophile to form bicyclic molecules and rings.

diene: A molecule that contains two alternating double bonds. A reactant in the Diels-Alder reaction.

dienophile: A reactant in the Diels-Alder reaction that contains a double bond. Dienophiles are often substituted with electron-withdrawing groups.

dipole moment: A measure of the separation of charge in a bond or molecule.

doublet: Describes an NMR signal split into two peaks.

eclipsed conformation: Conformation about a carbon-carbon single bond in which all of the bonds off of two adjacent carbons are aligned with each other (0^o apart when viewed in a Newman projection).

E isomer: Stereoisomer in which the two highest priority groups are on opposite sides= of a ring or double bond.

E1 elimination reaction: A reaction that eliminates a hydrohalic acid (like HCl, HBr, etc) to form an alkene. A first order reaction that goes through a carbocation mechanism.

E2 elimination reaction: A reaction that eliminates a hydrohalic acid (like HCl, HBr, etc) to form an alkene. A second order reaction that occurs in single step, in which the double bond is formed as the hydrohalic acid is eliminated.

electronegativity: A term describing the electron piggishness of an atom. More technically, a measure of the tendency of an atom to attract the electrons in a covalent bond to itself.

electrophile: Electron lover. A molecule that can accept a lone pair of electrons (a Lewis acid).

enantiomers: Molecules that are nonsuperimposable mirror ima= ges of each other.

equatorial: The bonds in a chair cyclohexane that are oriented along the equator of the ring.

ester: A molecule containing a carbonyl group adjacent to an oxygen (RCOOR'). Also a functional group.

ether: A molecule containing oxygen singly-bonded to two carbon atoms. Also a functional group. Ether often refers to diethyl ether.

fingerprint region: Region of an IR spectrum below 1,500 cm^-1. The fingerprint region of the IR spectrum is often complex and difficult to interpret.

functional group: A reactivity center.

gauche conformation: A type of staggered conformation in which two big groups are next to each other

halide: A member of the VIIA column of the periodic table (like F, Cl, Br, I, etc). Or a molecule that contains one of these atoms. Also a functional group.

Hückel's rule: A rule that states that completely conjugated planar rings with 4n+2 pi electrons are aromatic.

hybrid orbitals: Orbitals formed from mixing together atomic orbitals, like the sp^x orbitals, which result from mixing s and p orbitals.

hyperconjugation: Weak interaction (electron donation) between sigma bonds with p orbitals. Hyperconjugation explains why alkyl substituents stabilize carbocations.

inductive effects: Electron donation or withdrawal by electropositive or electronegative atoms through the sigma bond framework.

intermediate: Any species formed in a reaction on the way to making the product. Typically, intermediates are unstable.

ionic bond: Bond in which the electrons are unshared between two atoms.

IR spectrosco py: An instrumental technique that measures IR light absorption by molecules. Can be used to determine functional groups in an unknown molecule.

isolated double bonds: Double bonds separated by more than one carbon-carbon single bond.

J value: The coupling constant between two peaks in an NMR signal. Given in units of Hz.

ketone: A compound that contains a carbonyl group attached to two carbons. Also a functional group.

kinetic product: The product that forms the fastest. (This product has the lowest energy of activation.)

kinetics: The study of reaction rates.

Lewis acid:An electron pair acceptor.

Lewis base:An electron pair donor.

Markovniknov?s rule: A rule that states that electrophiles add to the less highly substituted carbon of a carbon-carbon double bond (or the carbon with the most hydrogen atoms).

mass spectrometry: An instrumental technique involving the ionization of molecules into fragments. Can be used to determine the molecular weights of unknown molecules.

meso compounds: Molecules that have chiral centers but are achiral as a result of one or more planes of symmetry in the molecule.

meta: Describes the positions of two substituents on a benzene ring that are separated by one carbon.

meta-directing substituent: Any substituent on an aromatic ring that directs in coming electrophiles to the meta position.

molecular ion: The fragment in a mass spectrum that corresponds to the cation radical (M+)of the molecule. The molecular ion gives the molecular mass of the molecule.

molecular orbital theory: Model for depict ing the location of electrons that allows electrons to delocalize across the entire molecule. A more accurate but less user-friendly theory than the valence-bond model.

multistep synthesis: Synthesis of a compound that takes several steps to achieve.

n+1 rule: Rule for predicting the coupling for a proton = in ¹H NMR spectroscopy. An NMR signal will split into n+1 peaks, where n is the number of equivalent adjacent protons.

natural product: A compound produced by a living organism.

nitrile: A compound contain a cyano group: a carbon triply-bonded to a nitrogen (CN). Also a functional group

NMR: Nuclear magnetic resonance sprectroscopy. A technique th at measures radiofrequency light absorption by molecules. A powerful structure-determining method.

node: A region in an orbital with zero electron density.

nucleophile: Nucleus lover. A molecule with the ability to donate a lone pair of electrons (a Lewis base)

nucleophilicity: A measure of the reactivity of a nucleophile in a nucleophilic substitution reaction.

organic compound: Carbon-containing compound.

optically active: Rotates plane-polarized light.

orbital: The region of space in which an electron is confined (the electron ?apartment?).

ortho: Describes the positions of two substituents on a benzene ring that are on adjacent carbons.

ortho-para director: An aromatic substituent that directs incoming electrophiles to the ortho or para positions.

para: Describes the poitions of two substituents on a benzene ring that are separated by two carbons.

phenyl ring: A benzene ring as a substituent. Abbreviated Ph.

pi bond (a.k.a. p bond): A bond with electron density above and below the two atoms, but not directly between the two atoms. Found in double and triple bonds.

pKa:The scale for defining a molecule's acidity (pKa =-log Ka).

plane-polarized light: Light that oscillates in a single plane.

plane of symmetry: A plane cutting through a molecule in which both halves are mirror images of each other.

protic solvent: A solvent that contains O-H or N-H bonds.

proton: An H⁺ ion. Also a positively-charged nuclear particle.

R group: Abbreviation given to an unimportant part of a molecule. Indicates Rest of molecule.

racemic mixture: A 50:50 mixture of two enantiomers. Racemic mixtures are optically inactive (don't rotate plane-polarized light).

radical: An atom or molecule with an unpaired electron.

resonance structures: Structures used to better depict the location of pi and nonbonding electrons on a molecule. A molecule looks like a hybrid of all resonance structures.

s-cis conformation: A conformation in which the two double bonds of a conjugated diene are on the same side of the carbon-carbon single bond that connects them. The required conformation for the Diels-Alder reaction.

s-trans conformation: The conformation in which the two double bonds of a conjugated diene are on opposite sided of the carbon-carbon single bond that connects them.

sigma bond (a.k.a. s bond): A bond in which electrons are located between the nuclei of the bonding atoms. Single bonds are sigma bonds.

singlet: Describes an NMR signal consisting of only one peak.

S_N1 reaction: A first order substitution reaction that goes through a carbocation intermediate.

S_N2 reaction: A second order substitution reaction that takes place in one step and has no intermediates.

sp: A hybrid orbital made by mixing one s orbital and one p orbital.

sp²: A hybrid orbital made by mixing one s orbital and two p orbitals.

sp³: A hybrid orbital made by mixing one s orbital and three p orbitals.

staggered conformation: Conformation about a carbon-carbon single bond in which bonds off of one carbon are at a maximum distance apart from bonds coming off of an adjacent carbon (60^odg apart when viewed in a Newman projection).

stereochemistry: Study of molecules in three dimensions.

stereoisomers: Molecules that have the same atom connectivity, but different orientations = of those atoms in three-dimensional space.

steric hindrance: Term referring to the way that atoms can shield a site by getting in the way of approach of a reactant.

substituent: A piece that sticks off of the main carbon chain or ring.

syn addition: A reaction in which two groups of a reagent X-Y add on the same face of a carbon-carbon double bond.

tautomers: Molecules that differ in the placement of a hydrogen and double bonds and are easily interconvertible. Keto and enol forms are tautomers.

thermodynamics: Study of the energies of molecules.

thermodynamic product: The reaction product with the lowest energy..

thiol:A molecule containing an SH group. Also a functional group.

transition state: The highest point on the energy hill that takes one species into another.

triplet: Describes an NMR signal split into three peaks.

Z isomer: Isomer in which the two highest-priority substituents are on the same side of a double bond or ring.

chimanshu_007

good one

congrats bro.......

shubhayan_c

gr8 yaar

Ask & Discuss Questions with Community & Experts