Basic principles

 In IUPAC nomenclature, a number of prefixes, suffixes and infixes are used to describe the type and position of functional groups in the compound.

  For many compounds, naming can begin by determining the name of the parent hydrocarbon and by identifying any functional groups in the molecule that

  distinguish it from the parent hydrocarbon. The numbering of the parent alkane is used, as modified, if necessary, by application of the Cahn Ingold Prelog

  priority rules ("CIP") in the case that ambiguity remains after consideration of the structure of the parent hydrocarbon alone. The name of the parent

  hydrocarbon is modified by the application of the highest-priority functional group suffix, with the remaining functional groups indicated by numbered

  In many cases, lack of rigor in applying all such nomenclature rules still yields a name that is intelligible — the aim, of course, being to avoid any ambiguity

  in terms of what substance is being discussed.

  For instance, strict application of CIP priority to the naming of the compound

            NH₂CH₂CH₂OH

  would render the name as 2-aminoethanol, which is preferred. However, the name 2-hydroxyethanamine unambiguously refers to the same compound.

  How the name was constructed:

       1.    There are two carbons in the main chain; this gives the root name "eth".

       2.    Since the carbons are singly-bonded, the suffix begins with "an".

       3.    The two functional groups are an alcohol (OH) and an amine (NH₂). The alcohol has the higher atomic number, and takes priority over the amine.

           The suffix for an alcohol ends in "ol", so that the suffix is "anol".

       4.    The amine group is not on the carbon with the OH (the #1 carbon), but one carbon over (the #2 carbon); therefore we indicate its presence

            with the prefix "2-amino".

  There is also an older naming system for organic compounds known as common nomenclature, which is often used for simple, well-known compounds,

  and also for complex compounds whose IUPAC names are too complex for everyday use.

  Simplified molecular input line entry specification (SMILES) strings are commonly used to describe organic compounds, and as such are a form of

  'naming' them.

  Alkanes

  Straight-chain alkanes take the suffix "-ane" and are prefixed depending on the number of carbon atoms in the chain, following standard IUPAC numerical multiplier  

  rules. The first few are:

  For example, the simplest alkane is CH₄ methane, and the nine-carbon alkane CH₃(CH₂)₇CH₃ is named nonane. If one was to name the 157-carbon alkane

  CH₃(CH₂)₁₅₅CH₃ the name would be heptapentahectane.

  Parentheses are used to indicate the repetition of the enclosed molecule (ie. (CH₂)₁₅₅ indicates that a molecule contains a chain of 155 CH₂ groups.)

   Cyclic alkanes are simply prefixed with "cyclo-", for example C₄H₈ is cyclobutane and C₆H₁₂ is cyclohexane.

    Branched alkanes are named as a straight-chain alkane with attached alkyl groups. They are prefixed with a number indicating the carbon the group

   is attached to, counting from the end of the alkane chain. Infixed is the name of the substituent, as for alkanes in the table above, plus "-yl". For

   example, (CH₃)₂CHCH₃, commonly known as isobutane, is treated as a propane chain with a methyl group bonded to the middle (2) carbon, and

  given the systematic name 2-methylpropane. Numbers may be dropped when there is no ambiguity, so 2-methylpropane is just methylpropane. (1-methylpropane

  would be identical to butane.)

    If there is ambiguity in the position of the substituent, depending on which end of the alkane chain is counted as "1", then numbering is chosen so

      that the smallest number is used. For example, (CH₃)₂CHCH₂CH₃ (isopentane) is named 2-methylbutane, not 3-methylbutane. Since this resolves

       the ambiguity, the number is again dropped in this case.
 

        If there are multiple side-branches of the same size alkyl group, their positions are separated by commas and the group prefixed with di-, tri-, tetra-,

        etc., depending on the number of branches (e.g. C(CH₃)₄ 2,2-dimethylpropane). If there are different groups, they are added in alphabetical order,

       separated by commas or hyphens: 3-ethyl-4-methylhexane. The longest possible main alkane chain is used; therefore 3-ethyl-4-methylhexane

       instead of 2,3-diethylpentane, even though these describe equivalent structures. The di-, tri- etc. prefixes are ignored for the purpose of alphabetical

       ordering of side chains (e.g. 3-ethyl-2,4-dimethylpentane, not 2,4-dimethyl-3-ethylpentane). If multiple chains of the longest possible length exist, the

        chain that has a larger number of branch points is the chain that is used.

Subsidiary branches off a side-chain are prefixed according to a secondary numbering system specific to that side branch, numbering from the point of attachment to the main chain, and then the whole side-branch is parenthesised and treated as a single substituent. For example, 4-(1-methylethyl)octane is an octane chain with a side chain bonded to the 4th carbon, the side chain consisting of an ethyl group with a methyl group attached to the carbon closest to the main chain.

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   Alkenes and Alkynes

      Alkenes are named for their parent alkane chain with the suffix "-ene" and an infixed number indicating the position of the double-bonded carbon in the chain: CH₂=CHCH₂CH₃ is but-1-ene. Ethene (ethylene) and propene (propylene) do not require infixed numbers, since there is no ambiguity in the structures. As before, the lowest number is used.

   Multiple double bonds take the form -diene, -triene, etc., with the size prefix of the chain taking an extra "a": CH₂=CHCH=CH₂ is buta-1,3-diene. Simple cis and trans isomers are indicated with a prefixed cis- or trans-: cis-but-2-ene, trans-but-2-ene. More complex geometric isomerisations are described using the Cahn Ingold Prelog priority rules.

     Alkynes are named using the same system, with the suffix "-yne" indicating a triple bond: ethyne (acetylene), propyne (methylacetylene).

     Alcohols

       Alcohols (R-OH) drop the terminal "e" from the name of the parent alkane, and take the suffix "-ol" with an infix numerical bonding position: CH₃CH₂CH₂OH is propan-1-ol. (Methanol and ethanol are unambiguous and do not require position numbers). The suffixes -diol, -triol, -tetraol, etc., are used for multiple -OH groups: Ethylene glycol CH₂OHCH₂OH is ethane-1,2-diol.

   If higher precedence functional groups are present (see order of precedence, below), the prefix "hydroxy" is used with the bonding position: CH₃CHOHCOOH is 2-hydroxypropanoic acid.

   Halogens (Alkyl Halides)

     Halogen functional groups are prefixed with the bonding position and take the form fluoro-, chloro-, bromo-, iodo-, etc., depending on the halogen. Multiple groups are dichloro-, trichloro-, etc, and dissimilar groups are orded alphabetically as before. For example, CHCl₃ (chloroform) is trichloromethane. The anesthetic Halothane (CF₃CHBrCl) is 2-bromo-2-chloro-1,1,1-trifluoroethane.

     Ketones

     In general ketones (R-CO-R) take the suffix "-one" (pronounced own, not won) with an infix position number: CH₃CH₂CH₂COCH₃ is pentan-2-one. For common ketones some traditional names such as acetone and benzophenone predominate, and these are acceptable IUPAC names, although some introductory chemistry texts use alternative names for acetone such as propan-2-one or propanone (see diagram). Additionally, in such unambiguous cases as propanone, the infixed number can be dropped. If a higher precedence suffix is in use, the prefix "oxo-" is used: CH₃CH₂CH₂COCH₂CHO is 3-oxohexanal.

    Aldehydes

   Aldehydes (R-CHO) take the suffix "-al". Since they are always at the end of an alkane chain, they do not need a position number: HCHO (formaldehyde) is methanal, CH₃CHO (acetaldehyde) is ethanal. If other functional groups are present, the chain is numbered such that the aldehyde carbon is in the "1" position.

   If a prefix form is required, "oxo-" is used (as for ketones), with the position number indicating the end of a chain: CHOCH₂COOH is 3-oxopropanoic acid. If the carbon in the carbonyl group cannot be included in the attached chain (for instance in the case of cyclic aldehydes), the prefix "formyl-" or the suffix "-carbaldehyde" is used: C₆H₁₁CHO is cyclohexanecarbaldehyde.

     Carboxylic acids

    In general carboxylic acids are named with the suffix -oic acid (etymologically a back-formation from benzoic acid). As for aldehydes, they take the "1" position on the parent chain, but do not have their position number indicated. For example, CH₃CH₂CH₂CH₂COOH (valeric acid) is named pentanoic acid. For common carboxylic acids some traditional names such as acetic acid are in such widespread use they are considered retained IUPAC names, although "systematic" names such as ethanoic acid are also acceptable. For carboxylic acids attached to a benzene ring such as Ph-COOH, these are named as benzoic acid or its derivatives.

  If there are multiple carboxyl groups on the same parent chain, the suffix "-carboxylic acid" can be used (as -dicarboxylic acid, -tricarboxylic acid, etc.). In these cases, the carbon in the carboxyl group does not count as being part of the main alkane chain. The same is true for the prefix form, "carboxyl-". Citric acid is one example; it is named 2-hydroxypropane- 1,2,3-tricarboxylic acid, rather than 2-carboxy, 2-hydroxypentanedioic acid.

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     Ethers

       Ethers (R-O-R) consist of an oxygen atom between the two attached carbon chains. The shorter of the two chains becomes the first part of the name with the -ane suffix changed to -oxy, and the longer alkane chain become the suffix of the name of the ether. Thus CH₃OCH₃ is methoxymethane, and CH₃OCH₂CH₃ is methoxyethane (not ethoxymethane). If the oxygen is not attached to the end of the main alkane chain, then the whole shorter alkyl-plus-ether group is treated as a side-chain and prefixed with its bonding position on the main chain. Thus CH₃OCH(CH₃)₂ is 2-methoxypropane.

      Esters (R-CO-O-R') are named as alkyl derivatives of carboxylic acids. The alkyl (R') group is named first. The R-CO-O part is then named as a separate word based on the carboxylic acid name, with the ending changed from -oic acid to -oate. For example, CH₃CH₂CH₂CH₂COOCH₃ is methyl pentanoate, and (CH₃)₂CHCH₂CH₂COOCH₂CH₃ is ethyl 4-methylpentanoate. For esters such as ethyl acetate (CH₃COOCH₂CH₃), ethyl formate (HCOOCH₂CH₃) or dimethyl phthalate that are based on common acids, IUPAC recommends use of these established names, called retained names. The -oate changes to -ate. Some simple examples, named both ways, are shown in the figure above.

   If the alkyl group is not attached at the end of the chain, the bond position to the ester group is infixed before "-yl": CH₃CH₂CH(CH₃)OOCCH₂CH₃ may be called but-2-yl propanoate or but-2-yl propionate.

     Amines and Amides

      Amines (R-NH₂) are named for the attached alkane chain with the suffix "-amine" (e.g. CH₃NH₂ methanamine). If necessary, the bonding position is infixed: CH₃CH₂CH₂NH₂ propan-1-amine, CH₃CHNH₂CH₃ propan-2-amine. The prefix form is "amino-".

    For secondary amines (of the form R-NH-R), the longest carbon chain attached to the nitrogen atom becomes the primary name of the amine; the other chain is prefixed as an alkyl group with location prefix given as an italic N: CH₃NHCH₂CH₃ is N-methylethanamine. Tertiary amines (R-NR-R) are treated similarly: CH₃CH₂N(CH₃)CH₂CH₂CH₃ is N-ethyl-N-methylpropanamine. Again, the substituent groups are ordered alphabetically.

      Amides (R-CO-NH₂) take the suffix "-amide". There is no prefix form, and no location number is required since they always terminate a carbon chain, e.g. CH₃CONH₂ (acetamide) is named ethanamide.

       Cyclic compounds

     Cycloalkanes and aromatic compounds can be treated as the main parent chain of the compound, in which case the position of substituents are numbered around the ring structure. For example, the three isomers of xylene CH₃C₆H₄CH₃, commonly the ortho-, meta-, and para- forms, are 1,2-dimethylbenzene, 1,3-dimethylbenzene, and 1,4-dimethylbenzene. The cyclic structures can also be treated as functional groups themselves, in which case they take the prefix "cycloalkyl-" (e.g. "cyclohexyl-") or for benzene, "phenyl-".

   The IUPAC nomenclature scheme becomes rapidly more elaborate for more complex cyclic structures, with notation for compounds containing conjoined rings, and many common names such as phenol, furan, indole, etc. being accepted as base names for compounds derived from them.

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     Order of precedence of groups

    When compounds contain more than one functional group, the order of precedence determines which groups are named with prefix or suffix forms. The highest precedence group takes the suffix, with all others taking the prefix form. However, double and triple bonds only take suffix form (-en and -yn) and are used with other suffixes.

   Prefixed substituents are ordered alphabetically (excluding any modifiers such as di-, tri-, etc.), e.g. chlorofluoromethane, not fluorochloromethane. If there are multiple functional groups of the same type, either prefixed or suffixed, the position numbers are ordered numerically (thus ethane-1,2-diol, not ethane-2,1-diol.) The N position indicator for amines and amides comes before "1", e.g. CH₃CH(CH₃)CH₂NH(CH₃) is N,2-dimethylpropanamine.

    *Note: These suffixes, in which the carbon atom is counted as part of the preceding chain, are the most commonly used. See individual functional group articles for more details.

              Common nomenclature - trivial names

   Common nomenclature is an older system of naming organic compounds. Instead of using the prefixes for the carbon skeleton above, another system is used. The pattern can be se

     Ketones

    Common names for ketones can be derived by naming the two alkyl or aryl groups bonded to the carbonyl group as separate words followed by the word ketone.

     Acetone

        Acetophenone

      Benzophenone

        Ethyl isopropyl ketone

        Diethyl ketone

     The first three of the names shown above are still considered to be acceptable IUPAC names.

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     Aldehydes

    The common name for an aldehyde is derived from the common name of the corresponding carboxylic acid by dropping the word acid and changing the suffix from -ic or -oic to -aldehyde.

        Formaldehyde

        Acetaldehyde

   The IUPAC nomenclature also provides rules for naming ions.

    Hydron

    Hydron is a generic term for hydrogen cation; protons, deuterons and tritons are all hydrons.

    Parent hydride cations

   Simple cations formed by adding a hydron to a hydride of a halogen, chalcogen or nitrogen-family element are named by adding the suffix "-onium" to the element's root: H₄N⁺ is ammonium, H₃O⁺ is oxonium, and H₂F⁺ is fluoronium. Ammonium was adopted instead of nitronium, which commonly refers to NO₂⁺.

   If the cationic center of the hydride is not a halogen, chalcogen or nitrogen-family element then the suffix "-ium" is added to the name of the neutral hydride after dropping any final 'e'. H₅C⁺ is methanium, HO-O⁺H₂ is dioxidanium (HO-OH is dioxidane), and H₂N-N⁺H₃ is diazanium (H₂N-NH₂ is diazane).

    Cations and substitution

   The above cations except for methanium are not, strictly speaking, organic, since they do not contain carbon. However, many organic cations are obtained by substituting another element or some functional group for a hydrogen.

    The name of each substitution is prepended to the hydride cation name. If many substitutions by the same functional group occur, then the number is indicated by prepending "di-", "tri-" as with halogenation. (CH₃)₃O⁺ is trimethyloxonium. CH₃F₃N⁺ is trifluoromethylammonium.

    Types of hydrocarbons

   The classifications for hydrocarbons defined by IUPAC nomenclature of organic chemistry are as follows:

      1.   Saturated hydrocarbons (alkanes) are the most simple of the hydrocarbon species and are composed entirely of single bonds and are saturated with hydrogen; they are the basis of petroleum fuels and are either found as linear or branched species of unlimited number. The general formula for saturated hydrocarbons is C_nH_2n+2 (assuming non-cyclic structures).

       2.   Unsaturated hydrocarbons have one or more double or triple bonds between carbon atoms. Those with one double bond are called alkenes, with the formula C_nH_2n (assuming non-cyclic structures). Those containing triple bonds are called alkynes, with general formula C_nH_2n-2.

      3.   Cycloalkanes are hydrocarbons containing one or more carbon rings to which hydrogen atoms are attached. The general formula for a saturated hydrocarbon containing one ring is C_nH_2n

      4.   Aromatic hydrocarbons, also known as arenes, are hydrocarbons that have at least one aromatic ring.

    Hydrocarbons can be gases (e.g. methane and propane), liquids (e.g. hexane and benzene), waxes or low melting solids (e.g. paraffin wax and naphthalene) or polymers (e.g. polyethylene, polypropylene and polystyrene).

    General properties

    Because of differences in molecular structure, the empirical formula remains different between hydrocarbons; in linear, or "straight-run" alkanes, alkenes and alkynes, the amount of bonded hydrogen lessens in alkenes and alkynes due to the "self-bonding" or catenation of carbon preventing entire saturation of the hydrocarbon by the formation of double or triple bonds.

      This inherent ability of hydrocarbons to bond to themselves is referred to as catenation, and allows hydrocarbon to form more complex molecules, such as cyclohexane, and in rarer cases, arenes such as benzene. This ability comes from the fact that bond character between carbon atoms is entirely non-polar, in that the distribution of electrons between the two elements is somewhat even due to the same electronegativity values of the elements (~0.30), and does not result in the formation of an electrophile.

        enerally, with catenation comes the loss of the total amount of bonded hydrocarbons and an increase in the amount of energy required for bond cleavage due to strain exerted upon the molecule; in molecules such as cyclohexane, this is referred to as ring strain, and occurs due to the "destabilized" spatial electron configuration of the atom.

         In simple chemistry, as per valence bond theory, the carbon atom must follow the "4-hydrogen rule", which states that the maximum number of atoms available to bond with carbon is equal to the number of electrons that are attracted into the outer shell of carbon. In terms of shells, carbon consists of an incomplete outer shell, which comprises 4 electrons, and thus has 4 electrons available for covalent or dative bonding.

        According thermodynamics studies hydrocarbons are stable in great depths within the earth. Hydrocarbons also have great abundance in the universe. In Titan (a Saturn moon) there are lakes and seas of liquid methane and ethane confirmed by Cassini-Huygens Mission.^{[citation needed]}

   Simple hydrocarbons and their variations

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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

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