Alcohols and Phenols
Alcohols and Phenols CHEM 2030 - 01
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CHEM 2030 - 01
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This 7 page Class Notes was uploaded by Shannon Z. on Monday October 26, 2015. The Class Notes belongs to CHEM 2030 - 01 at University of Missouri - Columbia taught by Rainer Glaser in Fall 2015. Since its upload, it has received 22 views. For similar materials see Survey of Organic Chemistry in Chemistry at University of Missouri - Columbia.
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Date Created: 10/26/15
1 Acidity and Basicity a Acids i BronstedLowry definition 1 Proton donors ii Lewis definition 1 Lewis acid a Substance that can accept a lone pair b Compounds with an incomplete valance shell an act as Lewis acids b Base i Bronsted Lowry Definition 1 Proton acceptor ii Lewis definition 1 Lewis base a Substance that can donate a lone pair b Any atom with an unshared electron pair can act as a Lewis base c Compounds containing atoms with incomplete valance shells can act as a Lewis base c Ampohoteric i Compounds that can act as both an acid and a base 1 Ex water d When an acid and base get together and an exchange of protons occurs a conjugate acid and conjugate base are created e Acid Strength i Measurement 1 Measured by acidity constant also known as ionization constant also known as Ka 2 The higher the value of Ka the stronger the acid 3 To prevent the value of Ka from being negative it is sometimes expressed as pKa a pKa is equal to the negative logarithm of Ka b pi log K c There is an inverse relationship between Ka and pKa 4 A larger pKa indicates a weaker acid ii There is an inverse relationship between acid strength and conjugate base strength 1 The stronger the acid the weaker the aconjugate base that is formed by an exchange of protons 2 Alcohols a What is an alcohol i Alcohols are characterized by an OH group 1 OH groups are called hydroxyl groups b Nomenclature of alcohols i Essentially the same as naming most other compounds ii Write the location number of substituents followed by hyphen The location numbers of hydrozyl groups should go last iii The root name propane butane ethane ect follows with the suffix ol 3 2 l l 2 3 CH30H CHJCH30H CH3CH2CH20H CH339HCH3 OH methanol etha nol l propanol 2 propanol methyl alcohol ethyl alcohol npropyl alcohol isopropyl alcohol CH3 I 2H3CH2CH2CH20H HIHCH2H CH3CHCH20H CH3 l2 0H UH CH3 lbutanol 2hnunol 2mcthyl lpropanol Lmethyl 2propanol ubutyl alcohol secbum alcohol isobutyl alcohol tertbutyl alcohol H CH2CHCH20H 0quot 2 pmpcn l o cyclohexauol phenylmcthmnl iv allyl alcohol cyclohcxyl alcohol benzyl alcohol c Classification of alcohols i Classification of alcohols depends on the number of organic groups R groups containing a C are attached to the carbon atom that bears the hydroxyl group 1 Primary alcohols a Contain one R group 2 Secondary a Contain two R groups 3 Tertiary a Contain three R groups 3 Phenom a What makes a phenol i A hydroxyl group directly attached to an aromatic ring b Nomenclature of phenols i The same nomenclature rules apply for phenols as pretty much every other compound only the name will end in the suffix phenol ii BUT if there are one of the following additional substituents on the compound the hydroxyl group will be named as a substituent 1 Carboxylic acid 2 Aldehyde 3 Ketone functionality A EH m Iv ii39m p E iy i39mne nmldehyi le 4 he naniii acid 4 Comparing Phenols and Alcohols a Breaking the COH bond i Phenom 1 Difficult to break as the removal of the OH would leave a phenol cation which is very unstable The phenol does not want that to happen ii Alcohols 1 The OH bond is easily broken with an acid catalyst b 5N2 and 5N1 i Alcohol 1 Will undergo both 5N2 and 5N2 reactions H Phenol 1 Will undergo neither 5N2 nor 5N2 reactions 5 Hydrogen Bonding in Alcohols and Phenols a Hydrogen bonds are weaker than ordinary covalent bonds but they do make a large enough difference to raise the boiling point of alcohols and phenols b Process i The oxygen in a hydroxyl group will polarize the 0H bond due to it s higher electronegativity ii The polarization places a partial positive charge on the hydrogen atom and a partial negative charge 0 the oxygen atom iii The partial positive charge on the hydrogen atom and it s small size allow it to bond with another electronegative atom such as another oxygen atom iv This could allow two or more alcohols to become loosely bound through hydrogen bonds c This causes alcohols to have a higher boiling point than ethers and hydrocarbons with a similar molecular weight d To reach boiling point you have to supply enough heat to break the hydrogen bonds in addition to vaporizing the compound e Alcohols will easily bond to water via hydrogen bonds as well 6 Acidity of Phenols and Alcohols a Hydroxyl groups can act as a proton donor i Acids are proton donors b Alcohols i Alcohols are weaker acids than phenols ii When an alcohol is broken into a conjugate base and conjugate acid the conjugate base formed is called an alkoxide ion iii The more bulky an alcohol is the weaker it is as an acid c Phenols i Phenols are stronger acids than alcohols 1 This is because their ions are stabilized by resonance An alkoxide s charge is concentrated on the oxygen atom The phenol s charge is more delocalized d Inductive effect i When the carbon atom a substituent is attached to has a charge ii The substituent has a H charge perhaps caused by a difference in electronegativities iii The charge on the carbon will balance out the H charge on the substituent e Electronwithdrawing groups increase acidity i They do this by stabilizing the conjugate base f Electrondonating groups decrease acidity i They do this by destabilizing the conjugate base g The more stable an acid is the stronger it is as an acid 7 Basicity of Alcohols and Phenols a Because of the unshared electron pairs on the oxygen from the hydroxyl group alcohols and phenols are technically bases but they are weak Lewis bases b Alkoxides i Alkoxide the conjugate base of alcohols ii Alkoxies make strong bases c Because they are weak bases alcohols and phenols can be protonated by strong acids forming alkyloxonium ions i This protonation is the first step in two different reactions regarding alcohols 1 Dehydration of alcohols to alkenes a Dehydration the removal of H20 i The reverse of hydration of an alkene b An elimination reaction c Process i Protonation d 1 A hydrogen proton is removed from a carbon atom that is directly attached to the carbon atom bearing the hydroxyl group a See image from book equation 721 or 724 The removed H are in blue 2 A double bond is formed between the previously hydroxyl bearing carbon atom and the carbon atom the hydrogen proton was removed from 3 Secondary and tertiary alcohols have multiple carbon atoms that the hydrogen proton can come off of This results in multiple potential structures a The primarily formed structure is the one that has the longest carbon chain following the double bond ii After protonation alcohols can be dehydrated by adding heat with a strong acid present Occurs via E1 and E2 depending of the alcohol i Tertiary alcohols 1 E1 ii Primary Alcohols 1 E2 2 Formation of alkyl halides a b The alcohol reacts with a hydrogen halide to form a alkyl halide In these reactions the hydroxyl group is substituted with a halogen Tertiary Alcohols i Occurs fastest in tertiary alcohols ii 5N1 with a carbocation intermediate Primary Alcohols i Occurs slowly ii Must be heated for several hours in a concentrated hydrochloric acid with a Lewis Acid catalyst iii 5N2 Secondary Alcohols i Intermediate speed ii 5N1 and 5N2 Because formations of alkyl halides through this method take time with secondary and primary alcohols there are a few other options i OSC2 Thionyl Chloride eeH til e Cl r2 1te 5 e II It eat tltienryl chleritle 3 EUH pheephorue halide 1 The alcohol and OSCIZ react to from and inorganic ester eliminating the H from the alcohol hydroxyl groups and a Cl from the thionyl chloride making the hydroxyl group a goo leaving group 2 Nucleophilic substitution occurs 3 The reaction produces two gaseous products that leave behind an alkyl halide Ell Tquot El i 1 EH l 51 1quotll llll 51 LlI l l Eh lereew te eater it llermetlilele ii PX3 1 Phosphorus halides can also react with alcohols to form alkyl halides a 3 H3190 I Cl er em Step 1 lMleke inrgenictriteetel Eliminate 3 HR Step 2 Hlelidee f39rmedin Step 1 d SHE with get leaving grup lRDhlPt 39 Step 3 lP Df plus 3 prtene gives HlalF39I39ZJ3 8 Oxidation of alcohols to Aldehydes Ketones and Carboxylic Acids a Alcohols with at least one hydrogen atom attached to the hydroxyl brearing carbon atom can be oxidized to carbonyl compounds A common oxidizing agent is chromic anhydride dissolved in aqueous sulfuric acid Jones reagent and with acetone as a solvent The body uses enzymes to perform oxidations especially in the liver Primary Alcohols Oxidation of primary alcohols make aldehydes which can be further oxidized to make carboxylic acids m o o inkling A tiIirll39i11g R H R C H agent 39 7 l DH H primary acnh ol aldehyde carbmLj ia acid ii Special reagents can be used to stop the reaction at the aldehyde stage e Secondary Alcohols i Oxidation of secondary alcohols make ketones W l uxidizin 39 l 1 R R agent R E H H ii secondaryaleoltol kgtgj e f Tertiary Alcohols i By definition tertiary alcohols 3 R groups and one hydroxyl group have no room to put a hydrogen atom directly onto the hydroxyl bearing carbon atom Therefore tertiary alcohols do not take place in oxidation reactions in this manner g Oxidation State of Primary and Secondary Alcohols i Oxidation begins by removing hydrogens and adding a double bond between the original OH group and the carbon that attached it to the rest of the molecule the reactive carbon ii As the compound is oxidized another bond is formed between the reactive carbon and the now O that is being added iii This results in an increase in the number of bonds from the reactive carbon leading towards oxygen atoms This means that the oxidation state of that carbon atom has increased 9 Alcohols with more than one hydroxyl group i Glycol 1 A compound with two adjacent alcohol groups ii Ethylene glycol 1 Used in cars as antifreeze 2 Completely miscible in water 3 Has a high boilig point iii Glycerol 1 High boiling point and water soluble Sweet tasting 10 Oxidation of Phenols a Phenols can be oxidized into many useful products However phenols also function as antioxidants which prevent the oxidation of substances sensitive to air oxidations i They react with and destroy radicals
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