Secondary is a term used in

organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...

to classify various types of compounds (e. g. alcohols, alkyl halides, amines) or

reactive intermediates In chemistry, a reactive intermediate or an intermediate is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule. Only in exceptional cases can these co ...

(e. g. alkyl radicals, carbocations). An atom is considered secondary if it has two 'R' Groups attached to it. An 'R' group is a carbon containing group such as a

methyl In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...

(CH3 ). A secondary compound is most often classified on an

alpha carbon In the nomenclature of organic chemistry, a locant is a term to indicate the position of a functional group or substituent within a molecule. Numeric locants The International Union of Pure and Applied Chemistry (IUPAC) recommends the use of ...

(middle carbon) or a nitrogen. The word secondary comes from the root word 'second' which means two. This

nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal naming conventions, conventions of everyday speech to the i ...

can be used in many cases and further used to explain relative reactivity. The reactivity of molecules varies with respect to the attached atoms. Thus, a primary, secondary, tertiary and quaternary molecule of the same function group will have different reactivities.

Secondary Alcohols

Secondary alcohols are identified by the groups attached to the central carbon that is bonding with the alcohol (-OH) group. A secondary alcohol is a carbon with four substituents including a single hydrogen, two 'R' groups, and one hydroxyl/alcohol (-OH) group. If one of the carbons the hydroxyl group is attached to is allylic or benzylic, the alcohol can also be referred to as a secondary

allylic In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . ...

benzylic In organic chemistry, benzyl is the substituent or molecular fragment possessing the structure . Benzyl features a benzene ring () attached to a methylene group () group. Nomenclature In IUPAC nomenclature, the prefix benzyl refers to a substi ...

alcohol.

Secondary Alcohols and Reactions

When a molecule undergoes a chemical process in which it loses electrons or gains an additional bond with an oxygen atom, this is considered oxidation. The oxidation of secondary alcohols often gives rise to ketones, which is an oxygen double bonded to two 'R' groups. Alcohols participate in many other chemical reactions including:

dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord for a related one within a chord progression * Substitution (poetry), a variation in poetic scansion * "Substitution" (song), a 2009 song by Silversun Pi ...

and

esterification In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

. The reactivity of alcohols increases as the carbon becomes more saturated with 'R' groups.

Saturation Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry * Saturation, a property of organic compounds referring to carbon-carbon bonds **Saturated and unsaturated compounds ** Degree of unsaturation **Saturated fat or fatty aci ...

refers to bond order and number of bonds with a more saturated molecule having more single bonds to 'R' groups. Thus, secondary alcohols are more reactive than

primary Primary or primaries may refer to: Arts, entertainment, and media Music Groups and labels * Primary (band), from Australia * Primary (musician), hip hop musician and record producer from South Korea * Primary Music, Israeli record label Works * ...

but less reactive than

tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

. Alcohols are characterized by having a hydroxyl group; hydroxyl (-OH) groups are very polar groups because of the high electronegativity seen on the oxygen.

Secondary Amines

A secondary amine contain a middle nitrogen that bonds with a single hydrogen and two 'R' groups. These 'R' groups can be carbon containing molecules or any other atoms excluding hydrogen. Nitrogen by nature has five valence electrons and thus will have three bonds and one lone pair to allow for a full octet. This explains why now we only see three bonds to the nitrogen as seen below, unlike the secondary alcohol that had four bonds to the middle carbon.

Secondary Amines and Reactions

Secondary amines are involved in many reactions. They can participate in reactions with aldehydes or ketones to give carbinolamines then allowing dehydration to give the

enamine An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine. Enamines are versatile intermediates. : The word "enamine" is derived from the affix ''en''-, used as the suffix of alkene, and th ...

. Secondary amines are considered weak acids with a conjugate base of an amide. Similarly to alcohols, secondary amines are more reactive than primary amines but less reactive than tertiary or quaternary.

Secondary Amides

amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...

is a group in which a nitrogen is directly attached to a Carbon with a double bonded oxygen. Specifically, a secondary amide is seen when the nitrogen to another additional 'R' carbon containing molecule. The third bond is from the middle nitrogen to a single hydrogen atom as shown below. A secondary amide is very similar to a secondary amine as it has a middle nitrogen, one hydrogen bond, two more substituents, and a single lone pair on the nitrogen.

Secondary Amides and Reactions

Amides are generally weak bases and can partake in several reactions. Specifically, secondary amides participate in reactions such as tautomeric equilibria with

thioamides A thioamide (rarely, thionamide, but also known as thiourylenes) is a functional group with the general structure R–CS–NR′R″, where R, R′, and R″ are organic groups. They are analogous to amides but they exhibit greater multiple bond ch ...

, ortho

lithiation In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom ...

. They also do simple reactions such as de-protonation events using a strong base, which is the loss of the single proton bonded to the middle nitrogen.

Secondary Phosphines

Secondary phosphines have two 'R' groups attached to a middle phosphorus atom and again, a single hydrogen bond. When in a catalytic environment, secondary phosphines are unstable, this limits them from being used in

homogeneous catalysis In chemistry, homogeneous catalysis is catalysis by a soluble catalyst in a solution. Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the reactants, principally in solution. In contrast, heterogeneous catalysis ...

. Secondary is a general term used in chemistry that can be applied to many molecules, even more than the ones listed here; the principles seen in these examples can be further applied to other functional group containing molecules. The ones shown above are common molecules seen in many organic reactions. By classifying a molecule as secondary it then be compared with a molecule of primary or tertiary nature to determine the relative reactivity.

References

{{Navbox stereochemistry Chemical nomenclature