# 20.3 Aldehydes, ketones, carboxylic acids, and esters  (Page 2/9)

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## Oxidation and reduction in organic chemistry

Methane represents the completely reduced form of an organic molecule that contains one carbon atom. Sequentially replacing each of the carbon-hydrogen bonds with a carbon-oxygen bond would lead to an alcohol, then an aldehyde, then a carboxylic acid (discussed later), and, finally, carbon dioxide:

${\text{CH}}_{4}\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{CH}}_{3}\text{OH}\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{CH}}_{2}\text{O}\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{HCO}}_{2}\text{H}\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{CO}}_{2}$

What are the oxidation numbers for the carbon atoms in the molecules shown here?

## Solution

In this example, we can calculate the oxidation number (review the chapter on oxidation-reduction reactions if necessary) for the carbon atom in each case (note how this would become difficult for larger molecules with additional carbon atoms and hydrogen atoms, which is why organic chemists use the definition dealing with replacing C–H bonds with C–O bonds described). For CH 4 , the carbon atom carries a –4 oxidation number (the hydrogen atoms are assigned oxidation numbers of +1 and the carbon atom balances that by having an oxidation number of –4). For the alcohol (in this case, methanol), the carbon atom has an oxidation number of –2 (the oxygen atom is assigned –2, the four hydrogen atoms each are assigned +1, and the carbon atom balances the sum by having an oxidation number of –2; note that compared to the carbon atom in CH 4 , this carbon atom has lost two electrons so it was oxidized); for the aldehyde, the carbon atom’s oxidation number is 0 (–2 for the oxygen atom and +1 for each hydrogen atom already balances to 0, so the oxidation number for the carbon atom is 0); for the carboxylic acid, the carbon atom’s oxidation number is +2 (two oxygen atoms each at –2 and two hydrogen atoms at +1); and for carbon dioxide, the carbon atom’s oxidation number is +4 (here, the carbon atom needs to balance the –4 sum from the two oxygen atoms).

Indicate whether the marked carbon atoms in the three molecules here are oxidized or reduced relative to the marked carbon atom in ethanol:

There is no need to calculate oxidation states in this case; instead, just compare the types of atoms bonded to the marked carbon atoms:

(a) reduced (bond to oxygen atom replaced by bond to hydrogen atom); (b) oxidized (one bond to hydrogen atom replaced by one bond to oxygen atom); (c) oxidized (2 bonds to hydrogen atoms have been replaced by bonds to an oxygen atom)

Aldehydes are commonly prepared by the oxidation of alcohols whose –OH functional group is located on the carbon atom at the end of the chain of carbon atoms in the alcohol:

Alcohols that have their –OH groups in the middle of the chain are necessary to synthesize a ketone, which requires the carbonyl group to be bonded to two other carbon atoms:

An alcohol with its –OH group bonded to a carbon atom that is bonded to no or one other carbon atom will form an aldehyde. An alcohol with its –OH group attached to two other carbon atoms will form a ketone. If three carbons are attached to the carbon bonded to the –OH, the molecule will not have a C–H bond to be replaced, so it will not be susceptible to oxidation.

What is pressure
Why does carbonic acid don't react with metals
Why does carbonic acid don't react with metal
Some metals will react depending on their Standard Electrode Potential. Carbonic acid is a very weak acid (i.e. a low hydrogen ion concentration) so the rate of reaction is very low.
Paul
sample of carbon-12 has a mass of 6.00g. How many atoms of carbon-12 are in the sample
a sample of carbon-12 has a mass of 6.00g. How many atoms of carbon-12 are in the sample
an object of weight 10N immersed in a liquid displaces a quantity of d liquid.if d liquid displaced weights 6N.determine d up thrust of the object
how human discover earth is not flat
We don't fall off. If set off in any direction in a straight line and keep going. You'll end up back where you started.
earth is spherical
Unique
Also, every other planet is spherical as that is the most energy efficient shape. gravity pulls equally on all areas. Sphere.
what is an ion
an atom that loses or gains an electron. Atoms normally have the same number of protons and electrons, therefore there is no charge as each + cancels out each -. When an atom loses an electron, it has more protons that electrons. Therefore the ion is called positive.
When an atom gains electrons it has more of them than protons. Therefore the ion is negative. You cannot change the number of protons as this results in a different element.
Gaining or losing electrons is based around the octet rule. 8 electrons in the outer shell is the most stable electron configuration (for the first three rows in the periodic table. After that it gets confusing so don't worry) So all atoms want to achieve this configuration.
Wat is chemical bonding
how to determine the number of atoms and the mass of zirconium, silicon, and oxygen found in 0.3384 mol of zircon4
what is a catalyst
A substance that speeds up the rate of a given reaction but does not react with any reactants
Brandon
something that speeds up a chemical reaction without being used up itself. It lowers the activation energy
something that speed up a chemical reaction without its self been used
Zainab
A catalyst is a substance that alters the rate of a reaction.. Meaning it can slow down a reaction or speeden it but it remains unchanged at the end of the reaction
Stellamaris
anything that speed up the rate of chemical reaction but it not being produced or consumed by the reaction
IBRAHIM
Faraday's first law of electrolysis state that...
the mass of a substance librated during electrolysis is directly proportional to the quantity of electricity passing through the electrolyte
Zainab
nice
Owolabi
greeaat
Abdul
another question
Owolabi
ys
Abdul
good
olanrewaju
gud one pls write it mathematically
Lekan
How can ionic bonds dissociate in aqueous solution
Because of the polarity of both ionic compounds and water the ionic compound will dissolve as "like dissolves like", and the molecule forms bonds with the water.
Claud
are all aqueous solutions water contained?
blossom
No, but a lot are.
Claud
it dissociate when d metal is combined wit oxygen
Lekan
I wanna understand more about isomers
Isomers are essentially the same molecules of one particular substance, except with different bonding points along the molecule. if you want a better example, look up xylene, p-xylene, and m-xylene. isomers are more for organic chemistry
Aaron
what is catenation
The property of carbon to form long chain with other atom!
Lareb
hydrocarbons can be classified as..1.Aliphatic compounds 2.cyclic compounds.under aliphatic compounds there are two types saturated hydrocarbons(alkanes) and unsaturated hydrocarbons(alkenes and alkynes).
thanks but i have also heard of aromatic hydrocarbons
emmanuel
so am kinda confused
emmanuel
how
Emmanuel
hydrocarbons are classified into 2 namely: aliphatic compound and aromatic compound
Mgbachi
aliphatic compound and aromatic compound
Mgbachi