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 7 Dehydration Alcohol heat 8 Oxidation pri Alcohol Pri Alcohol O 9 Oxidation sec Alcohol Sec Alcohol O 10 Oxidation aldehyde Aldehyde O 11 Ether Synthesis Alcohol alcohol O H O H C H 3 H H 2 2 H C C H 3 C C C C H H C C C H 3 H O C H 3 3 H OA C C H 3 H 2 H C H 2 B C 3C H H 2C 3D 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 H C H 3 2 H H 2 H O C 3C C C H O H C C H H C C H 3 3 3 C C H H 3 2 C H C H 3 H C C H H OA 3 C H 3 BH O C H H C C C H E 3 3 C H 3 H 3O CC HD 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 Func gp Formula Structure Name Rank Ques 4 Polarity of Functional Groups relatively constant number of C H s salt amide acids Aldehyde amine ester ether ketone C4H7O2 M C3H7NO C3H6O2 C3H6O C4H11N C4H8O2 C3H18O 1 2 3 4 5 6 7 alkane C4H10 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 H C H 3 2 H H C 2C H O C 3C C C H O H C C H H C C H 3 3 3 H H 3 2 C H C H 3 H C C H H OA 3 B C H 3 H O C H H C C C H E 3 3 C H 3 C H C3 O HD 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 H C H 3 2 H H C 2 H O C 3C C C H O H C C H H C C H 3 3 3 C H H 3 2 C H C H 3 H C C H H OA 3 B C H 3 H O C H …