Structure And Properties Of Ketones Biology Essay

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Ketones are sp2 hybridized, and have trigonal planar geometry, with C-C-O and C-C-C bond angles of 120 degrees. The oxygen in the carbonyl group is more electronegative than the carbonyl carbon therefore carbonyl group is polar s a result. Ketones are also soluble in water because of interaction of water with the carbonyl group. Ketones are a lot more volatile than alcohols and carboxylic acids, due to the inability of ketones to serve both as hydrogen-bond and acceptors.

There are two main reasons why α-hydrogen of a carbonyl is acidic. Firstly, α- carbon is adjacent to one or more partially positive carbon atoms. The α carbon, too Partakes of some of this positive charge (in-ductive effect by electron-withdrawal), and C-H bonds are consequently weakened. Secondly, and more important, is the resonance stabilization of the enolate ion, the anion formed when the proton is lost.

"Hydrogen bonded to a sp3 hybridized carbon adjacent to a carbonyl carbon is much more acidic than hydrogen's bonded to other sp3 hybridized carbons. For example the pka for dissociation of an α-hydrogen from an aldehyde or ketones ranges from 16 to 20, and the pka for dissociation of an α-hydrogen from an ester is about 25[1

1.5 Characterisation of Ketones

1.5.1 Infrared spectroscopy (IR spectroscopy)

IR is commonly used to ascertain the types of functional groups. Groups such as C=O, C=C bond, a aromatic ring, a carbon-carbon triple bond can all be determined with infrared spectroscopy. IR can also provide information about which functional groups are missing. However, IR cannot provide information on the number of hydrogens in the molecule, and a accurate sturutral determination isn't isn't made.

Table 1: Table of Infrared Bands

Class of compound

Functional Group

Wavenumber (cm-1)

























Different bonds belonging to different groups within the molecule will vibrate at different frequencies and many organic functional groups can be readily identified by their IR absorption properties. The stronger the bond, the higher the vibration frequency. Hence double bond vibrate at higher frequencies than single bonds like pairs of atoms, and stronger bonds such as O-H, N-H and C-H vibrate at higher frequencies than weaker bonds such as C-C and C-O[2]

1.5.2 Nuclear Magnetic Resonance Spectroscopy (NMR)

The numbers hydrogen in the molecule and chemical environment information are provided by high-resolution nuclear magnetic resonance chemical shifts and spin-spin splitting. Spatial positions information is provided by the chemical nature of hydrogen which is identified by the chemical shifts. Spin-spin interactions produced by multiplicities bands can also provide more information on spatial positions. When a known sample has similar chemical shifts and relatives intensities of an unknown sample then identification can be made.

Curtin and co-workers [3], showed that nuclear magnetic resonance spectroscopy can be used to differentiate between aldehydes and ketones, based on the absence of the aldehydic hydrogen in their 2,4-dinitrophenylhydrazone and semicarbazone derivatives.

"Nuclear magnetic resonance spectroscopy (NMR) measures the absorption of "light" energy in the radiofrequency portion of the electromagnetic spectrum [4]

1.5.3 Carbon-13 NMR

1.6 Organic tests

Brady's test

Aldehydes and ketones functional groups can be detected by using 2, 4-dinitrophenylhydrazine, a yellow or red colour precipitate (dinitophenylhydrazone) indicates a positive result

RR'C=O + C6H3 (NO2)2NHNH2 → C6H3 (NO2)2NHNCRR' + H2O

The reaction can be considered to be like a addition-elimination reaction, where the -NH2 group attaches to the C=O group, and a water molecule is removed. The reaction mechanism of 2, 4-dinitrophenylhydrazine is shown below:

"This test is useful for identifying aldehydes and Ketones" (Addison Ault, Techniques and experiments for organic chemistry, sixth edition, pp253, printed in USA)

Synthesis of Ketones

Kornblum-DeLaMare rearrangement

Kornblum-DeLaMare rearrangement is an important in biosynthesis of prostaglandins. When primary or secondary peroxide goes through an organic reaction process under base catalysis condition, bases such as potassium hydroxide or triethylamine condition it is converted to a ketone and an alcohol.


Nef Reaction

In a Nef reaction an aldehyde or ketone and nitrous oxide are produced by acid hydrolysis of a salt of a primary or secondary nitroalkane. In 1893 Konovalov (Konovalov.,: J. Russ. Phys. Chem. Soc. pp2, 1893, 6(I), 509), converted potassium salt of 1-phenylnitroethane with sulphuric acid to acetophenone.

+ ½ N20 + ½ H20 + NAH


Freidel-Crafts acylation


Chromate Oxidation

Oxidation of alcohols is basically a two step process. The first step involves the formation of chromate esters. Alcohols react with carboxylic acids, phosphoric acid, and sulfonic acids to produce various types of esters. The same is true for chromic acid and PCC; they react with alcohols to produce chromate esters. Once the chromate ester is formed, it undergoes an elimination reaction to generate the carbonyl group of the aldehyde or ketone. These two steps are outlined in below.

Reaction of Ketones

Addition of Hydrogen Cyanide

Addition of Organometallic Reagents

Alkyl lithium and Grignard reagents are the two most reagents that are used. They are both strong and powerful nuclophiles and bases, so they have the ability of forming a bond to carbonyls groups insuring an alkoxide salts are produced. Below are few reactions shown of carbonyl compounds reacting with organometallic reagents.

Addition of Alcohols: Formation of Hemiactelas and Acetals

Alcohols can add to ketones in the same manner as water. Addition of the alcohol molecule with the carbonyl group leads to the formation of a hemiacetal (a half-acetal).

The addition of alcohol across the carbonyl π bond of an aldehyde or ketone takes place by a pathway essentially identical to that for the addition of water. These additions can be catalyzed by either base or acid (M. A. Fox and J. K. Whitesell, Organic Chemistry, second edition,(1947)

Base-Catalyzed formation of a Hemiacetal Mechanism

Acid-Catalyzed formation of a Hemiacetal Mechanism

"The mechanism of hemiacetal formation involves three steps. First, the carbonyl oxygen is protonated by the acid catalyst. The alcohol oxygen then attacks the carbonyl carbon and a proton is lost from the resulting positive oxygen. Each step is reversible" (Organic Chemisrty, Hart,craine,hart)

R2C=O + ROH RO-(R2) C-O-H (a hemiacetal)

Acetal formation

Two equivalents of alcohol and elimination of water reaction can form the product acetals, which are geminal-diether derivatives of Ketones and Aldehydes.

Acetal formation is best achieved when a catalysed is used and the water which is produced is removed from the reaction. Acetal formation are said to be reversible, acetals can be hydrolysed back by addition of an acid. Below is a mechanism of a acetal formation and acetal hydrolysis.

Formation of imines and Enamines

Imines formation

Imines are made when an aldehyde or ketone reacts with ammonia or primary-amines derivatives. This reaction is reversible as it is acid-catalyzed and water is eliminated.

Enamine formation

Enamines are also formed when a secondary amine reacts with a ketone or aldehyde. This reaction is an acid catalysed reaction in which by water is lost. Below are two diagrams in which the reaction is represented.


The infra-red spectrum of 4-(bromomethyl) benzonitirle (starting material) is shown below in table 4.1


Bond Vibration

Structural Feature

1503.10 / 1511.45 / 1606.06

C=C stretch

Aromatic ring


CN stretch

Nitrile ( cyanidos )

The IR spectrum corresponds to 4-(bromomethyl) benzonitirle (starting material). The data shows the presence of the aromatic ring from the regions 1503.10 / 1511.45 / 1606.06cm-1. So overall the data corresponds to the desired structure of 4-(bromomethyl) benzonitirle.

The infra-red spectrum of Dibenzylketone is shown below in table 4.2


Bond Vibration

Structural Feature

15997.10 / 16105.20

C=C Stretch

Aromatic ring


C=O Stretch


The IR spectrum corresponds to Dibenzylketone. The data shows the presence of the aromatic ring from the regions 15997.10 / 16105.20. So overall the data corresponds to the desired structure of to Dibenzylketone.

The infra-red spectrum of 1, 3-bis (4-cyanophenyl)-2-propanone is shown below in table 4.3


Bond Vibration

Structural Feature

1543.25/ 1604.91/ 1677.51

C=C Stretch

Aromatic ring


C=O Stretch



CN stretch

Nitrile ( cyanidos )

The IR spectrum corresponds to 1, 3-bis (4-cyanophenyl)-2-propanone to. The data shows the presence of the aromatic ring from the regions 15997.10 / 16105.20cm-1.Overall the data corresponds to the desired structure of to 1, 3-bis (4-cyanophenyl)-2-propanone.


Previous methods and analysis

Preparation of 1, 3-bis (4-cyanophenyl)-2-propanone

Preparation of 1, 3-bis (4-cyanophenyl)-2-propanone (ketone) can be prepared by convenient method where by using an alkyl halide as the starting compound. The method involves generation of a ferrate ion, Fe (CO) 4, from Fe (CO) 5 and aqueous sodium hydroxide in an organic solvent in the presence of a phase-transfer catalysed.

Experimental procedure

Under N2 in room temperature, mixtures of 4-(Bromomethyl)benzonitrile(0.80g), Fe (CO) 5 (0.80g), 33% of aqueous NaOH (6ml), and tetrabutylammonium bromide [Bu4NBr] (1g) in 6ml of toluene was stirred for a period of 24 hrs in a bottom rounded flask. The mixture was then poured onto I2-toluene (3.15g, 25cm3) and stirred for 0.5hrs. Aqueous Na2S2O3, 10% HCL, and water were all used to successively wash the mixture in the order mentioned. Magnesium sulphate was finally used to dry the toluene solution and evaporated in a rotary evaporator. TLC, infrared spectrum and percentage yield were all recorded from the residue.

Table 1 Preparation of symmetrical ketones (Chemistry letters, pp. 321-324, 1979.Published by the chemical society of Japan)


Reaction time, hrs



Benzyl bromide [1a]


Dibenzyl Ketone [2a]

94 (83)

Benzyl chloride




p-Chlorobenzyl bromide [1b]


Bis ( p-chlorobenzyl)

ketone [2b]

88 (70)

p-Methylbenzyl bromide [1c]


Bis ( p-methylbenzyl)

ketone [2c]

98 (77)

1-iodoctane [1d]


9-Heptadecanone [2d]


1-Bromoctane [1e]




Table 2: Dependence of the product distribution on the concentrations of NaOH in the reaction of [1c] with Fe (CO) 5

Concentration of NaOH (%)

Product distribution of [2c] (%)

Product distribution of [3c] (%)























Infrared spectrum of the staring material and dibenzylketone was tkaen, this helped ditiguish the bonds that were present and which ones where missing. I used dibenzylketone because it very similar to, 3-bis (4-cyanophenyl)-2-propanone but only has the CN group's missing. The infrared spectrum of, 3-bis (4-cyanophenyl)-2-propanone shows that I obtained the peaks that I was expecting to obtain. The peaks of a CN group at 2226.91 and aromatic (ring) peaks at 1677.51/1604.91/1543.25. The yield obtained was 45% which is quite low, but the desired structure was produced. A few of the attempts did not work due to human error ie the I2-toulene mixture was poured in to the reaction without separating the iodine from the toluene. Therefore there was a black solid that didn't dissolve during the successive washing, and with the constant usage of the solvent that was used to wash the mixture could have played a key role in the low yield. Improvement to the reaction was made, firstly in the flask itself, all the air was socked out from the flask to insure the reaction was in a complete N2 conditions.


The concentration of NaOH was very important in the reaction. High concentration of NaOH caused it to react with the CN group, before the ferrate ion was generated, causing it to form sodium salts which precipitated as a white solid in the flask and was not soluble. Further work of this reaction is needed, to see if there are any possible other reagents that can be used to give a better yield. Although I analysed my residue further by using H1NMR, due to technical difficulties the spectrum of the product was not obtained. Time was very limited, more organic analysis could have been done ie C13NMR which would of helped analysis the residue even further.


[1] P. Y. Bruice. Organic Chemistry, fourth edition, pp106, printed in USA

[2]L. M. Harwood, C. J. Moody and J. M. Percy, Experimental Organic Chemistry, Standard and Microscale, 2nd edition, (1989)

[3] D. Y. Curtin, J. A. Gourse, W. H. Richardson, and K. L. Rinehart, Jr.,J. Org. Chem., pp23-24, (1959)

[4]Addison Ault, Techniques and experiments for organic chemistry, fifth edition,pp 218, printed in USA)