Glossary - Appendixes - Organic Chemistry I For Dummies, 2nd Edition (2014)

Organic Chemistry I For Dummies, 2nd Edition (2014)

Part VI. Appendixes

Appendix C. Glossary

achiral:

A molecule that’s superimposable on its mirror 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 the 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 (see Figure C-1).

anti-aromatic:

A highly unstable planar ring system with 4n π electrons.

anti-periplanar (also known as 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 π 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) in a chair cyclohexane (see Figure C-2).

base:

A proton acceptor or an electron pair donor.

benzyl group:

A benzene ring plus a methylene (CH2) unit (C6H5—CH2).

benzylic position:

The carbon attached to a benzene ring.

benzyne:

A highly reactive intermediate. A benzene ring with a triple bond (see Figure C-3).

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 (see Figure C-4).

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 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 constant:

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

coupling protons:

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

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 (also known as δ 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 cyclohexene 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:

An NMR signal split into two lines.

E isomer:

Stereoisomer in which the two highest-priority groups are on opposite sides of a double bond.

E1 elimination reaction:

A reaction that eliminates an acid (like HCl, HBr, and so on) to form an alkene. A first-order reaction that goes through a carbocation mechanism. It is the preferred mechanism for dehydration of secondary and tertiary alcohols to form alkenes.

E2 elimination reaction:

A reaction that eliminates an acid (like HCl, HBr, and so on) 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.

eclipsed conformation:

Conformation about a carbon-carbon single bond in which all the bonds of two adjacent carbons are aligned with each other (0 degrees apart when viewed in a Newman projection). (See Figure C-5.)

electronegativity:

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:

An electron lover. A molecule that can accept a lone pair of electrons (a Lewis acid).

enantiomers:

Molecules that are nonsuperimposable mirror images of each other.

equatorial:

The bonds in a chair cyclohexane that are oriented along the equator of the ring (see Figure C-6).

ester:

A molecule containing a carbonyl group adjacent to an oxygen bound to a carbon (RCOOR). Also a functional group.

ether:

A molecule containing oxygen singly bonded to two carbon atoms (R-O-R). Also a functional group. 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 (shown in a Newman projection in Figure C-7).

halide:

A member of the VIIA column of the Periodic Table (like F, Cl, Br, I, and so on) 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 + 2π electrons are aromatic.

hybrid orbitals:

Orbitals formed from mixing together atomic orbitals, like the spx orbitals, which result from mixing s and p orbitals.

hyperconjugation:

Weak interaction (electron donation) between sigma bonds with p orbitals. Hyperconjugation helps explain why alkyl substituents stabilize carbocations.

inductive effects:

Electron donation or withdrawal by electropositive or electronegative atoms through the sigma bond framework. Inductive effects help explain why alkyl substituents stabilize carbocations.

intermediate:

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

ionic bond:

A bond in which the electrons are unshared between two atoms.

IR spectroscopy:

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 (RCOR). 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.

Markovnikov’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:

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

meta:

The positions of two substituents on a benzene ring that are separated by one carbon (see Figure C-8).

meta-directing substituent:

Any substituent on an aromatic ring that directs incoming 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:

A model for depicting 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:

A 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 containing a cyano group, a carbon triply bonded to a nitrogen (CN). Also a functional group.

NMR:

Nuclear magnetic resonance sprectroscopy. A technique that measures radio frequency light absorption by molecules. A powerful structure-determining method.

node:

A region in an orbital with zero electron density.

nucleophile:

A 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.

optically active:

Rotates plane-polarized light.

orbital:

The region of space in which an electron is confined (the electron “apartment”).

organic compound:

A carbon-containing compound.

ortho:

The positions of two substituents on a benzene ring that are on adjacent carbons (see Figure C-9).

ortho-para director:

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

oxidation:

A reaction that involves the loss of electrons by an atom or molecule.

para:

Describes the positions of two substituents on a benzene ring that are separated by two carbons (see Figure C-10).

phenyl ring:

A benzene ring as a substituent, sometimes abbreviated Ph.

pi bond (also known as π 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 of symmetry:

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

plane-polarized light:

Light that oscillates in a single plane.

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 the rest of the molecule.

Racemic mixture:

A 50/50 mixture of two enantiomers. Racemic mixtures are optically inactive (they don’t rotate plane-polarized light).

radical:

An atom or molecule with an unpaired electron.

reduction:

A reaction involving the gain of electrons by an atom or molecule.

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 (see Figure C-11). 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 sides of the carbon-carbon single bond that connects them (see Figure C-12).

sigma bond (also known as σ 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 line.

SN1 reaction:

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

SN2 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. The angle between sp orbitals is usually about 180 degrees.

sp2

A hybrid orbital made by mixing one s orbital and two p orbitals. The angle between sp2 orbitals is usually about 120 degrees.

sp3:

A hybrid orbital made by mixing one s orbital and three p orbitals. The angle between sp3 orbitals is usually about 109.5 degrees.

staggered conformation:

Conformation about a carbon-carbon single bond in which bonds of one carbon are at a maximum distance apart from bonds coming off of an adjacent carbon (60 degrees apart when viewed in a Newman projection). (See Figure C-13.)

stereochemistry:

The 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:

The way that atoms can shield a site by getting in the way of approach of a reactant.

substituent:

A piece that sticks off 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.

thermodynamic product:

The reaction product with the lowest energy.

thermodynamics:

The study of the energies of molecules.

thiol:

A molecule containing an SH group. Also, a functional group.

transition state:

The structure that corresponds to the highest point on the energy hill that takes one species into another.

triplet:

An NMR signal split into three lines.

Z isomer:

An isomer in which the two highest-priority substituents are on the same side of a double bond.

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FIGURE C-1: A Newman projection of an anti conformation.

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FIGURE C-2: Axial bonds.

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FIGURE C-3: Benzyne.

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FIGURE C-4: Chair conformation.

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FIGURE C-5: A Newman projection of eclipsed conformation.

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FIGURE C-6: Equatorial.

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FIGURE C-7: A Newman projection of a gauche conformation.

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FIGURE C-8: Meta.

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FIGURE C-9: Ortho.

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FIGURE C-10: Para.

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FIGURE C-11: s-cis conformation.

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FIGURE C-12: s-trans conformation.

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FIGURE C-13: A Newman projection of a staggered conformation.