Chapter 16 16 7 Addition of Alcohols Hemiacetals and Acetals o Hemiacetal formation Exam 3 Study Guide Aldehydes and ketones laso undergo addition rxns in which an alc combines with the carbonyl carbon and oxygen Products are hemiacetals have both alcohol like OH group and ether like OR group bonded to what was once carbonyl carbon atom The H from the alcohol bonds to the carbonyl group oxygen and the OR from the alcohol bonds to the carbonyl group carbon The negatively polarized alcohol oxygen atom adds to the positively polarized carbonyl carbon The reaction is reversible o Hemiacetals rapidly revert back to aldehydes or ketones by loss of alcohol and establish an equilibrium with the aldehyde or ketone Hemiacetals are often too unsable to be isolated unless they form from the same molecule cyclic Most simple sugars exist as cyclic hemiacetals i e glucose o Acetal Formation If a small amount of acid catalyst is added to the rxn of an alcohol with an aldehyde or ketone the hemiacetal initially formed is converted into an acetal in a substitution rxn Acetal compound that has two ether like OR groups bonded to what was the carbonyl carbon atom o Acetyl Hydrolysis Acetal formation is an equilibrium rxn So the extent to which the rxn proceeds in either direction can be controlled by changing the rxn conditions The aldehyde or ketone from which an acetal is formed can be regenerated by reversing the rxn Reversal simply requires an acid catalyst and large quantity of water to drive the rxn back toward the aldehyde or ketone The rxn of an acetal with water is an example of hydrolysis a rxn in which a bond or bonds are broken and the H and OH of water add to the atoms of the broken bond or bonds The first step of formation of an acetal is as the water breaks one of the C OR bonds and a C OH bond is formed in its place The carbonyl group is then formed The result is the ketone or aldehyde from which the acetal was made plus 2 molecules of alcohol RO H Although acetals and hemiacetals react with water in the presence of acid they are unreactive under basic conditions Chapter 17 17 8 Phosphoric Acid Derivatives o Phosphoric acid is an inorganic acid with 3 acidic hydrogen atoms It can form 3 different anions OH molecules Phosphoric acid H3PO4 double bond to O three single bonds to three Dihydrogen phosphate ion H2PO4 double bond to O two single bonds to two OH molecules one bond to O atom Hydrogen phosphate ion HPO4 2 one double bond to O one single bond to one OH molecule two single bonds to two O atoms Phosphate ion PO4 3 one double bond to O three single bonds to O atoms esters o Phosphoric acid like carboxylic acid reacts with alcohol to form phosphate May be esterified at one two or all three of its OH groups Phosphoric acid alcohol phosphate ester water o Phosphate monoesters and diesters are acidic because they still contain acidic hydrogen atoms They are most often present as ions Phosphate groups usually written in ionized forms o Phosphoryl group PO3 o If 2 mlcls of phosphoric acid combine to lose water they form a phosphoric 2 acid anhydride Resulting acid reacts with another phosphoric acid mlcl to give a triphosphoric acid See deiagrams on page 541 These acids can also form esters known as diphosphates and o Phosphorylation transfer of a phosphoryl group form one molecule to triphosphates another o Phosphoryl groups often provided by ATP triphosphate which is coverted to diphosphate ADP in rxn accompanied by release of energy In the body this is used for regulating activity of biomolecules ADP Alcohol ROH ADP energy See rxn on p 541 Chapter 20 Intro o We are powered by oxidation of biomolecules made mainly of carbon hydrogen and oxygen End products are CO2 H2O and energy C H O food molecules O2 CO2 H2O energy o Principal food molecules lipids proteins and carbohydrates Broken down by individual pathways o The product of these pathways is usually acetyl coenzyme A 20 1 Energy and Life o Living things must do mechanical work Bending towards sunlight engulf food walk o And chemical work Synthesize biomolecules needed for Energy storage Growth Repair Replacement o Cells need energy for work of moving molecules and ions across cell membranes Energy released from food allows this to be done o Energy can be converted from one form to another but can neither be created nor destroyed o Energy used by living things ultimately comes from sum o Energy is stored in chemical bonds of fats o Some organism do not depend on sunlight for energy but use chemical energy instead o Releasing all of the energy at once would harm us o It is difficult to capture energy for storage once it has been converted to heat o Energy requirements Must be released from food gradually Must be stored in readily accessible forms Release of energy must be finely controlled so that it is available exactly when and where it is needed Just enough energy must be released as heat to maintain constant body temperature Energy in a form other than heat must be available to drive chemical rxns that are not favorable at body temperatures o Citric acid cycle and oxidative phosphorylation form the common pathway for the production of energy from all sources and for all needs o Everything you do uses cellular energy 20 2 Energy and Biochemical Rxns o Chemical rxns either release or absorb energy For a rxn to be favorable it is dependent on either the release or absorption of energy as heat change in enthalpy H and increase or decrease in disorder S the entropy change caused by rxn G H T S o Reactions in living organisms are no different from rxns in a chemistry lab They follow the same laws have same energy requirements o Spontaneous rxns favorable in forward direction release free energy and energy released is available for work Described as exergonic are source of biochemical energy Exergonic release of free energy represented by G Exothermic only applies to release of heat represented by H o Transformed values of G are used for standard state conditions Typically indicated by symbol G G to symbolize free energy change of biochemical rxns o Products of a favorable exergonic rxn are farther downhill on energy scale than reactants products are more stable than reactants o As a result free energy change has a negative value G o Oixdation rxns are usually downhill rxns that release energy o Oxidation of glucose produces 686 kcal 2870 kJ of free energy per mol of glucose o The greater the amount of free energy released the