Lecture 7 Flashcards
(16 cards)
Alcohols
It is any organic compound in which a hydroxyl OH- group is bounded to carbon atom of an alkyl or substituted alkyl.
Alcohols are derivatives of water in which on of the hydrogen atoms are replaced with an alkyl group R
(R-O-H) — the hydroxyl functional group strongly contributes to the physical properties of alcohols.
Nomenclature
IUPAC name: replace “e” from alkanes with “ol”
Common name: the name of the alkyl group followed by alcohol
Naming alcohols
- Select the longest chain that contains the -OH group. If there is a chain with more carbons than the one containing the OH group it will be named as a substituent
- Number from the end which is nearest -OH group (lowest possible number to show the location of -OH
- Change the ending of the parent alkanes from “-e” to “-ol”, use the number to show the location of -OH
- Locate and name any other substituent (alphabetical order) as prefixes to the name of the main chain.
Classification of alcohols
Different -OH group of alkyl alcohols can be positioned on different carbon atoms of the carbon chain and are classified as primo ray, secondary and tertiary.
Diols and Triols
Depends on the number of -OH groups:
-Diol: contains two -OH hydroxyl groups
-Triol: contains three -OH hydroxyl groups
Glycols – alcohols with
two –OH groups on an
adjacent carbon atom
Properties of Alcohols
Solubility in Water:
(Higher the molecular weight, lower solubility)
As the chain or the R group increases the hydrocarbon (non-polar) characters of the compound minimises the polar character of the OH group
Part. 2
The solubility of an alcohol are affected by:
a) Length of the carbon chain
b) The shape of the molecule
(short chain alcohols are soluble in water, longer chains insoluble in water)!!!
The molecule which is more branched will be more soluble in water
and will have a lower boiling point than the straight chain isomer.
Alcohols and phenols are flammable (must be transported carefully)
Alcohols are weak acids (alkyl alcohol weaker than phenol).
Depending on the amount of OH groups
Part. 3
Alcohol’s physical properties depends on whether polar or nonpolar portion
dominates. Polar/nonpolar?
Electronegativity: C – O: (3.5 – 2.5 = 1.0)
C – H: (2.5 – 2.1 = 0.4)
O – H: (3.5 – 2.1 = 1.4)
Higher boiling point than alkanes with similar molecular mass, because they
form hydrogen bonds with one another
Hydrogen bonding occurs between molecules (represented by dashed line) –
this differs alkanes from alcohols, the hydroxyl group participate in hydrogen
bonding
Preparation of alcohols
- Alcohols are one of the most important molecules in organic chemistry.
They can be prepared from may different types of compounds and the can be converted into many different types of compounds.
The alcohol hydroxyl can be
converted to many other functional
groups!
(This makes alcohol useful in
synthesis)
Uses
Industrial:
Alcohols have an applications in industries such as food and beverage, as reagents or
as solvents. Low toxicity and ability to dissolve non-polar substances. Alcohols are
used in ethanol, perfumes and vegetable essences such as vanilla.
Medical:
Ethanol can be used as an antiseptic to disinfectant the skin before injections.
Ethanol-based soaps are becoming common (they do not require drying due to
volatility of the compound. Alcohol gels have become common as hand sanitizers.
(COVID )
Fuels:
Some alcohols, methanol and ethanol can be used as an alcohol fuel.
Performance can be increased in forced induction internal combustion engines by
injecting alcohol into the air intake after the turbocharger
or supercharger has pressurized the air. This cools the pressurized air, providing a
denser air, which allows for more fuel, and therefore more pow
Cyclic Hyrdocarbons
Cyclic; they contain rings or atoms
The carbohydrate we eat, the nucleotides that make up our DNA and RNA are cyclic, the antibiotics we use to treat diseases are cyclic.
General Formula:
Simple cycloalkanes are rings or CH2 groups (methylene groups). Each one has exactly twice as many hydrogen atoms as carbon atoms, giving the general molecular formula CnH2n
Physical properties of Cycloalkanes
Most cycloalkanes resemble the acyclic (noncyclic), open-chain alkanes in
their physical properties and in their chemistry.
• They are nonpolar, relatively inert compounds with boiling points and
melting points that depend on their molecular weights.
• The cycloalkanes are held in a more compact cyclic shape, so their
physical properties are similar to those of the compact, branched alkanes.
Cyclopropane was once used as general anesthetic because its vapors causes
sleepiness
Nomenclature of Cycloalkanes
Naming of all organic molecules follows the IUPAC system!
1. Identify the largest carbon chain (ring).
2. Number each carbon atom in the longest chain so that all substituents get the
lowest possible locant.
3. Identify and name any substituents and assign their locants. Don’t forget to take
the alphabetical order into consideration
Part 2
Note: the special case of an alkane composed
of both a ring and a long chain.
If the number of carbons in the ring is greater
than or equal to the number of carbons in the
longest chain, the compound is named as a
cycloalkane.
Part. 3
Naming of all organic molecules follows the IUPAC system!
For cycloalkenes;
1. Identify the longest carbon chain (ring) that contains the functional group (C=C).
2. The carbon atoms of the ring C=C bond are numbered 1 and 2 in the direction that gives
the substituent encountered first the smaller number.
3. Identify and name any substituents and assign their locants. Don’t forget to take the
alphabetical order into consideration
Configurational Isomerism
• Cis-isomers have substituents on the
same side of the double bond.
• Trans-isomers have the substituents on
the opposite side of the double bond.
Also applies to cycloalkanes:
• Cis-isomers have substituents on the
same side of the ring.
• Trans-isomers have the substituents on
the opposite side of the ring
