# Organic Chemistry/Ketones and aldehydes

Aldehydes (![](Aldehyde2.png "Aldehyde2.png"){width="50"}) and ketones
(![](Ketone-general.svg "Ketone-general.svg"){width="50"}) are both
carbonyl compounds. They are organic compounds in which the carbonyl
carbon is connected to conyl carbon satisfied by a H atom, while a
ketone has both its vacancies satisfied by carbon.

## Naming Aldehydes and Ketones

**Ketones** are named by replacing the**-e** in the alkane name with
**-one**. The **carbon chain** is numbered so that the ketone carbon,
called **the carbonyl group**, gets the lowest number. For example,
![](Butanone-structure-skeletal.png "Butanone-structure-skeletal.png"){width="50"}
would be named 2-butanone because the root structure is butane and the
ketone group is on the number two carbon.

Alternatively, functional class nomenclature of ketones is also
recognized by IUPAC, which is done by naming the substituents attached
to the carbonyl group in alphabetical order, ending with the word
ketone. The above example of 2-butanone can also be named ethyl methyl
ketone using this method.

If two ketone groups are on the same structure, the ending **-dione**
would be added to the alkane name, such as heptane-2,5-dione.

**Aldehydes** replace the**-e** ending of an alkane with **-al** for an
aldehyde. Since an aldehyde is always at the carbon that is numbered
one, a number designation is not needed. For example, the aldehyde of
pentane would simply be pentanal.

The **-CH=O group of aldehydes** is known as a formyl group. When a
formyl group is attached to a ring, the ring name is followed by the
suffix **\"carbaldehyde\"**. For example, a hexane ring with a formyl
group is named cyclohexanecarbaldehyde.

## Boiling Points and Bond Angles

**Aldehyde and ketone** polarity is characterized by the high dipole
moments of their carbonyl group, which makes them rather polar
molecules. They are more polar than alkenes and ethers, though because
they lack hydrogen, they cannot participate in hydrogen bonding like
alcohols, thus making their relative boiling points higher than alkenes
and ethers, yet lower than alcohols.

Typical bond angles between the carbonyl group and its substituents show
minor deviations from the trigonal planar angles of 120 degrees, with a
slightly higher bond angle between the O=C-R bond than the R-C-R bond on
the carbonyl carbon (with R being any substituent).

## Preparing Aldehydes and Ketones

### Preparing Aldehydes

#### Partial oxidation of primary alcohols to aldehydes

This reaction uses pyridinium chlorochromate (PCC) in the absence of
water (if water is present the alcohol will be oxidized further to a
carboxylic acid). ![](alcohol-aldehyde.PNG "alcohol-aldehyde.PNG")

#### From fatty acids

`<chem>`{=html}Ca(COOH)2 -\>\[\\Delta\] HCHO + CaCO3 `</chem>`{=html}

`<chem>`{=html}(CH3COO)2Ca -\>\[\\Delta\] CH3COCH3 +
CaCO3`</chem>`{=html}

`<chem>`{=html}(CH3COO)2Ca + (HCOO)2Ca -\> CH3CHO`</chem>`{=html}

#### Stephen reduction

`<chem>`{=html}R-CN + SnCl2 + HCl -\> R-CH=NH2+Cl- -\>\[H\^+/H_2O\]
R-CHO `</chem>`{=html}

Here sulfur is used as a poisoner so that aldehyde formed doesn\'t get
oxidised to the carboxylic acid. See the Wikipedia
article for more detail.

#### Rosenmund reaction

`<chem>`{=html}R-COCl + Pd + BaSO4 + S -\> R-CHO`</chem>`{=html}

(For solvent xylene is used)

### Preparing Ketones

#### From Grignard reagents

`<chem>`{=html}RCOOR\' + R\'MgX -\>RCOR + R\'OH`</chem>`{=html}

`                    R'            R'      OH  `\
`                    |             |       |`

`<chem>`{=html}RC=O + R\'MgX -\> R-CO-MgX -\> R-C-OH +
Mg-X`</chem>`{=html}

`|                   |             |  `\
`O-R'                OR'           OR'`

#### From nitriles

RCN + R\'MgX \-\-\--\> RCOR\'(after hydrolysis) HCN does not react with
RMgX as HCN has acidic hydrogen which results in RH being formed.

#### From gem dihalides

RCCl~2~R + strong base \-\-\--\> RCOR

#### Oppenaur oxidation

Reagent is Aluminium tert. butoxide solvent is acetone

ROH + ACETONE \-\-\--\> Ketone + isopropyl alcohol this oxidation does
not affect double bonds in this oxidation ketone act as a oxidizing
agent this is exact opposite to merrwine pondroff reduction

#### Friedel-Crafts acylation of aromatic compounds

An aromatic ring reacts with a carboxylic acid chlorine (RCOCl) in the
presence of AlCl~3~ to form an aryl ketone of the form ArCOR.

#### Oxidation of secondary alcohols to ketones

A secondary alcohol can be oxidised into a ketone using acidified
potassium dichromate(VI) and heating under reflux.

The orange dichromate(VI) ion, Cr2O72-, is reduced to the green Cr3+(aq)
ion.

### Ozonolysis of alkenes

It is a reaction in which the double bond is completely broken and the
alkene molecule converted into two smaller molecules.

!A generalized scheme of
ozonolysis{width="350"}
Ozonolysis (cleavage \"by ozone) is carried out in two stages: first,
addition of ozone to the double bond to form an ozonide ; and second,
hydrolysis of the ozonide to yield the cleavage products.

Ozone gas is passed into a solution of the alkene in some inert solvent
like carbon tetrachloride; evaporation of the solvent leaves the ozonide
as a viscous oil. This unstable, explosive compound is not purified, but
is treated directly with water, generally in the presence of a reducing
agent. If oxidising reagent is used, aldehyde or ketone if oxidisable
can further oxidise into carboxylic acid which is not the case with
reducing agents

In the cleavage products a doubly-bonded oxygen is found attached to
each of the originally doubly-bonded carbons.

The function of the reducing agent, which is frequently zinc dust, is to
prevent formation of hydrogen peroxide, which would otherwise react with
the aldehydes and ketones. (Aldehydes, RCHO, are often converted into
acids,rCOOH, for ease of isolation.)

##### Mechanism

The alkene and ozone form an intermediate molozonide in a 1,3-dipolar
cycloaddition. Next, the molozonide reverts to its corresponding
carbonyl oxide (also called the Criegee intermediate or Criegee
zwitterion) and aldehyde or ketone in a retro-1,3-dipolar cycloaddition.
The oxide and aldehyde or ketone react again in a 1,3-dipolar
cycloaddition or produce a relatively stable ozonide intermediate (a
trioxolane) !The reaction mechanism of
ozonolysis.{width="600"}

### Hydration of alkynes

Water is added to an alkyne in a strong acid. The strong acid used is
sulfuric acid and mercuric acid.

## Keto-enol tautomerism

In the presence of an acid (H+) or a base (OH-), the aldehyde or ketone
will form an equilibrium with enols, in which the double bond of the
carbonyl group migrates to form double bond between the carbonyl and the
alpha (α) carbon.

In the presence of an acid, protonation of the oxygen group will occur,
and water will abstract an alpha (α) hydrogen.

In the presence of a base, deprotonation of the alpha hydrogen will
occur, and a hydrogen from water will be abstracted by the carbonyl
oxygen.

This is an important feature of ketone and aldehydes, and is known as
the *keto-enolic tautomery* or *keto-enol tautomerism*, i.e. the
equilibrium of carbonyl compounds between two forms.

It must be stressed that the *keto* and the *enol* forms are **two
distinct compounds**, not isomers. They are known as tautomers of each
other. The presence of α-hydrogen is necessary for this equilibrium:
those compounds not possessing it are called *non-enolizable* ketones.

!Mechanism of enol-keto
tautomerism

## Reactions of Aldehydes and Ketones

### Reactions with the carbonyl carbon

Since aldehydes and ketones contain a polar carbonyl group, the
partially positive carbon atom can act as an electrophile. Strong and
weak nucleophiles are able to attack this carbonyl carbon, resulting in
a net addition to the molecule.

#### Nucleophilic addition

With cyanide, nucleophilic addition occur to give a hydroxynitrile:

RR\'C=O + CN^-^ + H^+^ → RR\'COHCN

e.g. propanone → 2-hydroxymethylpropanonitrile

### Reactions with the carbonyl oxygen

The partially negative oxygen can act as a nucleophile, or be attacked
by electrophiles.

### Oxidation

Using a strong oxidizing agent such as the Tollens\' Reagent (Ag~2~O in
aqueous ammonia) acidified dichromate, Benedict\'s/Fehling\'s reagent
(essentially alkaline Cu^+2^); aldehydes but not ketones may be oxidized
into carboxylic acids. This is one way to test for the presence of an
aldehyde in a sample compound: an aldehyde will become a carboxylic acid
when reacted with Tollens\' reagent, but a ketone will not react. when
aldehydes react with fehling solution a red precipitate is obtained (due
to formation of Cu~2~O) .

## Inductive Effect and Greek letter assignment

The carbonyl group is very electron withdrawing, and adjacent carbons
are effected by induction. Using the carbonyl group as a reference,
adjacent carbons are named using Greek letters in order of closeness to
the carbonyl group. Alpha (α) carbons are directly attached to the
carbonyl group, beta (β) carbons are connected to alpha carbons, gamma
(γ) to beta (β), and so on.

Due to the inductive effect of the partial positive especially prone to
removal.

id:Kimia Organik/Keton dan
aldehida
