Week # 3 Lecture # 7 and 8 - Alcohols, Phenols, and Thiols
Concepts: Classes of alcohols - (primary, secondary, tertiary), hydrogen bonding, polarity of all functional groups, solubility.
Reaction Summary:
4. Hydration: Alkene + water -à
7. Dehydration : Alcohol +heat à
8. Oxidation - pri. Alcohol: Pri. Alcohol + (O) à
9. Oxidation - sec. Alcohol: Sec. Alcohol + (O) à
10. Oxidation - aldehyde: Aldehyde + (O) à
11. Ether Synthesis: Alcohol + alcohol à
Types or Classes of Alcohols:
The alcohols may be classified according to the number of carbons
attached to the carbon with the -OH group.
Ques. 1: Write the IUPAC name of the alcohols above.
Primary alcohol: The -OH carbon has only one other carbon attached.
Example (A) above.
Secondary alcohol: The -OH carbon has two other carbons attached.
Example (B) above.
Tertiary alcohol: The -OH carbon has three other carbons attached.
Example (D) above
Ques. 2: What type of alcohol is (C) above?
Ques. 3: Classify the following alcohols and give the IUPAC names:
Polarity of Organic Compounds:
http://www.elmhurst.edu/~chm/vchembook/213organicfcgp.html
The greater the electronegativity difference between atoms in a bond, the more polar the bond. Partial negative charges are found on the most electronegative atoms, the others are partially positive. In general, the presence of an oxygen is more polar than a nitrogen because oxygen is more electronegative than nitrogen.
The combination of carbons and hydrogens as in hydrocarbons or in the hydrocarbon portion of a molecule with a functional group is always NON-POLAR.
Polarity and Boiling Point:
The polarity of the molecules determines the forces of attraction between the molecules in the liquid state. Polar molecules are attracted by the opposite charge effect (the positive end of one molecule is attracted to the negative end of another molecule. Molecules have different degrees of polarity as determined by the functional group present.
Principle: The greater the forces of attraction, the higher the boiling point; or the greater the polarity, the higher the boiling point.
Ques. 4: Polarity of Functional Groups (relatively constant number of C, H's)
Func gp / salt / amide / acids / Aldehyde ketone / amine / ester / ether / alkaneFormula / C4H7O2-M+ / C3H7NO / C3H6O2 / C3H6O / C4H11N / C4H8O2 / C3H18O / C4H10
Structure
Name
Rank / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8
An abbreviated polarity list to know well is:
Amide > Acid > Alcohol > Amine > Ether > Alkane
HYDROGEN BONDING
Introduction: The hydrogen bond is really a special case of dipole forces. A hydrogen bond is the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge. The hydrogen then has the partial positive charge.
To recognize the possibility of hydrogen bonding, examine the Lewis structure of the molecule. The electronegative atom must have one or more unshared electron pairs as in the case of oxygen and nitrogen, and has a negative partial charge. The hydrogen, which has a partial positive charge tries to find another atom of oxygen or nitrogen with excess electrons to share and is attracted to the partial negative charge. This forms the basis for the hydrogen bond.
Hydrogen Bond Definition: The hydrogen on one molecule attached to O or N that is attracted to an O or N of a different molecule.
In the graphic on the left, the hydrogen is partially positive and attracted to the partially negative charge on the oxygen. Because oxygen has two lone pairs, two different hydrogen bonds can be made to each oxygen. This is a very specific bond as indicated. Some combinations which are not hydrogen bonds include: hydrogen to another hydrogen or hydrogen to a carbon.
Ques. 5: Draw an example of three water molecules engaged in hydrogen bonding.
Ques. 6: Write the structure of methanol and then draw three molecules of methanol engaged in hydrogen bonding.
Ques. 7: Draw the figure for hydrogen bonding between two or three ethanol molecules.
Ques. 8: An ether molecule is also a derivative of a water molecule. Both hydrogens have been replaced by carbons.
a) Write the structure for dimethyl ether and diethyl ether.
b) Is hydrogen bonding between ether molecules possible?
Solubility - "Likes dissolve Likes" - Application of Polarity
Solubility is a measure of the ability of two substances to dissolve in each other. The relative solubility of one compound in another depends largely on the type and strength of intermolecular bonds between the molecules in the pure compounds. If the bonding strength between molecules of substance A is roughly equal to the intermolecular forces of substance B, substances A and B will probably be soluble in each other.
For example, methyl alcohol dissolves in water because the hydrogen bonds between water molecules and those between alcohol molecules are of roughly equal strength. The hydrogen bonds between similar molecules can be broken and replaced by hydrogen bonds between alcohol and water molecules. Alcohol molecules can "slip" into the network of hydrogen bonds in water. Both molecules have polar O-H bonds. The attraction of opposite partial charges allows the mixing of water and alcohol molecules - such compounds are said to be hydrophilic-"water loving.
Ques. 9: Draw several water and methanol molecules hydrogen bonded together
On the other hand, hydrocarbons and water are not soluble in each other. Hydrocarbon alkanes do not have any hydrogen bonds nor any polar attractions. Thus the only appreciable attractions are between water molecules, so they effectively "squeeze out" the hydrocarbon molecules. At the same time the hydrocarbon molecules tend to prefer "their own company" and effectively keep out water molecules. These compounds are said to be hydrophobic-"water hating". Hydrocarbons have non-polar carbon-carbon and carbon-hydrogen bonds. The behavior of alkane or hydrocarbon parts in all molecules imparts a non-polar character to the molecule.
Solubility principle:
The above relationships are usually summed up by the common generalization: "Likes dissolve Likes". This means that a polar solvent will dissolve polar compounds but will not dissolve non-polar compounds.
The generalization "likes dissolve likes" must be applied carefully. For example, all alcohols are polar yet not all alcohols are soluble in water. The structure of the alcohols must be carefully examined. The -OH part is polar and imparts water solubility. On the other hand, the hydrocarbon part is non-polar and imparts water insolubility. The relative dominance of one part over the other determines the overall behavior of the molecule. If the hydrocarbon part is dominant, this results in a non-polar molecular behavior. If the -OH polar part dominates, the molecule is essentially polar and water soluble.
Ques. 10: Explain in detail the reasons for the solubility data
in the table below. Write structures for each alcohol.
Solubility Of Alcohols In Water
Solubility at 20oC
Alcohol Structure g. ROH/100g. H2O
a. Ethanol completely soluble
b. 1-propanol completely soluble
c. 1-butanol 8.0
d. 1-pentanol 2.7
e. 1-hexanol 0.6
QUES. 11: Which compound is more soluble in hexane?
1- heptanol or 1-pentanol; Explain.
Ques. 12: Which compound is more soluble in water?
Pentanoic acid or 2-pentanol. Explain
Ques. 13: Which compound is more soluble in gasoline (octane)?
Diethyl ether or 2-butanol. Explain.
Ques. 14: Write the structures for :
Methanethiol (smell of chedder cheese); 1-propanethiol (smell of onions)
Ques. 15: Write the structures for:
Phenol, 3-hydroxyphenol (resourcinol - antiseptic), 2-phenylphenol (Lysol)
Ques. 16: Addition Reaction
4. Hydration(HOH / Alkene + water à alcohol*Markovnikov's Rule / Propene + HOH à
2-propanol
Ques. 17: Subtraction Reactions - Dehydration and Oxidation
Reaction Name / Word Equation / Example7. Dehydration / Alcohol +heat
à allkene + water / 2-propanol à propene + HOH
8. Oxidation - pri. alcohol / Pri. Alcohol + (O)
à aldehyde + water / 1-propanol + (O) à propanal
9. Oxidation - sec. alcohol / Sec. Alcohol + (O)
à ketone + water / 2-propanol + (O) à
2-propanone
10. Oxidation - aldehyde / Aldehyde + (O) à Acid / Propanal + (O) à propanoic acid
Ques. 18: Combination Reactions
(generally remove a water molecule to combine two molecules)
Reaction Name / Word Equation / Example11. Ether Synthesis / Alcohol + alcohol
à ether + water / Ethanol + ethanol à
diethyl ether + HOH
Ques. 19: Dehydration: Name the reactants.
a.
b
c.
d.
Ques. 20: Oxidations - Name the Reactants
a
b.
c.
d.
e.
f.
21. Write the structures for the products and give the names of both.
C.
D.