318-10 - Organic Organic Lecture Series CH 318 N LECTURE 10...

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Unformatted text preview: Organic Organic Lecture Series CH 318 N LECTURE 10 Textbook Assignment: Chapter 16 Homework (for credit): POW 5 posted Today’s Topics: Aldehydes/Ketones-properties Notice & Announcements: Pick up Exams (after class) WEL 2.212 1 Organic Lecture Series Carbenes & Carbenoids • Carbene, R2C: a neutral molecule in which a carbon atom is surrounded by only six valence electrons • Methylene, the simplest carbene – prepared by photolysis or thermolysis of diazomethane + H2 C N N: : hν H2 C : + : N N: Methylene (th e simp lest carben e) – methylene prepared in this manner is so nonselective that it is of little synthetic use 2 Organic Organic Lecture Series Carbenes & Carbenoids Dichlorocarbene – prepared by treating chloroform with potassium tert-butoxide CHCl3 + (CH3 ) 3 CO K Trichlorometh ane Potas sium (Cloroform) t ert -b utoxid e + Cl2 C: + (CH3 ) 3 COH + K Cl D ichlorocarbe ne tert -Bu tyl alc oh ol + - 3 Organic Lecture Series Dichlorocarbene reacts with alkenes to give dichlorocyclopropanes H Cl 2 C: Dichlorocarbene ( CH3 ) 3 CO - K + H + CCl2 H A dichlorocyclopropane Cl + cis- 3-Hexene HCCl 3 H Cl cis- 1,1-Dichloro2,3-diethylcyclopropane 4 Organic Organic Lecture Series • Simmons-Smith reaction Simmons– a way to add methylene to an alkene to form a cyclopropane – generation of the Simmons-Smith reagent CH 2 I 2 Diiodomethane + Zn( Cu) Zinc-copper couple diethyl ether ICH 2 ZnI Iodomethylzinc iodide (Simmons-Smith reagent) – this organozinc compound reacts with a wide variety of alkenes to give cyclopropanes (prepared by: Zn dust; CuCl & heat) 5 Organic Lecture Series Simmons-Smith reaction: the organozinc compound reacts with an alkene by a concerted mechanism* I CH2 I Zn ZnI 2 + H2C *concerted mechanism-one in which there is simultaneous bond breaking and bond formation. 6 Organic Organic Lecture Series Uses of the Simmons-Smith reagent: Zn(Cu) + CH2 I2 Methylenecyclopentan e O Zn(Cu) + CH2 I2 2-Cyclohexenone diethyl ether + ZnI2 diethyl ether Spiro[4.2]h eptane O H CH2 + ZnI2 H Bicyclo[4.1.0]h eptan-2-one 7 Organic Lecture Series Naltrexone opioid receptor antagonist used primarily in the management of alcohol dependence and opioid dependence. 8 Organic Organic Lecture Series Aldehydes And Ketones Ketones 9 Organic Lecture Series The Carbonyl Group The next units cover the physical and chemical properties of classes of compounds containing the carbonyl group, C=O C=O aldehydes and ketones (Chapter 16) carboxylic acids (Chapter 17) acid halides, acid anhydrides, esters, amides (Chapter 18) enolate anions (Chapter 19) 10 Organic Organic Lecture Series – the carbonyl group consists of one sigma bond formed by the overlap of sp2 hybrid orbitals and one pi bond formed by the overlap of parallel 2p orbitals – pi bonding and pi antibonding MOs for formaldehyde 11 Organic Lecture Series – the functional group of an aldehyde is a carbonyl group bonded to a H atom and a carbon atom – the functional group of a ketone is a carbonyl group bonded to two carbon atoms O HCH Methanal (Formaldehyde) O O CH3 CH Ethanal (Acetaldehyde) CH3 CCH3 Propanone (Acetone) 12 Organic Organic Lecture Series Nomenclature IUPAC names: • the parent chain is the longest chain that contains the functional group • for an aldehyde, change the suffix from -e to -al • for an unsaturated aldehyde, change the infix from -an- to -en-; the location of the suffix anendetermines the numbering pattern • for a cyclic molecule in which -CHO is bonded to the ring, add the suffix -carbaldehyde carbaldehyde 13 13 Organic Lecture Series O H 3-Meth ylb utanal O 7 O 5 6 4 3 2 1 H 8 H 2-Propen al (2E)-3,7-D imeth yl-2,6-octad ienal (A crolein ) (Geran ial) CHO Cy cl o pe n tane carb aldehyde CHO HO 4 1 CHO trans -4-Hyd roxycyclohexan ecarbald ehyde C6 H5 CHO Benzald ehyde t rans-3-Ph enyl-2-prop enal (Cin namaldeh yd e) 14 Organic Organic Lecture Series IUPAC names • the parent alkane is the longest chain that contains the carbonyl group • for ketones, change the suffix -e to -one • number the chain to give C=O the smaller number • the IUPAC retains the common names acetone, acetophenone, acetophenone, and benzophenone O O O O Prop anone (Aceton e) A cetophen on e Benzophen on e 1-Phenyl-1-pen tanone 15 Organic Lecture Series Common Names – for an aldehyde, the common name is derived from the common name of the corresponding carboxylic acid – for a ketone, name the two alkyl or aryl groups bonded to the carbonyl carbon and add the word ketone O HCH Formaldehyde O O HCOH Formic acid O CH3 CH A cetaldeh yd e O O O CH3 COH Acetic acid Ethyl isopropyl ketone D iethyl ketone D icyclohexyl ketone 16 Organic Organic Lecture Series Physical Properties Oxygen is more electronegative than carbon (3.5 vs 2.5) and, therefore, a C=O group is polar – aldehydes and ketones are polar compounds and interact in the pure state by dipole-dipole interaction – they have higher boiling points and are more soluble in water than nonpolar compounds of comparable molecular weight 17 Spectral Properties Organic Lecture Series • IR: Carbonyl-Aldehydes 1720-1725; also show m C-H @ 2720; Ketones 1710-1715 (aryl ketones 1680) • NMR: Aldehydes 9.5-10.2 (s) ketones protons protons α to 2.1-2.3 can be 2.2-2.6 • 13CNMR: carbonyl carbon 180-215 ppm • MS: Aldehydes (M-1) loss of aldehyde H; loss of CO (M-28); both groups undergo α cleavage 18 Organic Organic Lecture Series 1680 19 Organic Lecture Series O b c a c d c b m, 2 H cd m, 3 H a s, 3 H b 20 Organic Organic Lecture Series 1710 21 Organic Lecture Series S, 1H O b m, 1H d a c d c b H a c m, 2H m, 2H b 400mHz 22 Organic Organic Lecture Series Reaction Themes One of the most common reaction themes of a carbonyl group is addition of a nucleophile to form a tetrahedral carbonyl addition compound (intermediate). R Nu - O C O Nu C - + R R R Tetrahedral carbonyl add ition comp ou nd 23 Reaction Themes Organic Lecture Series A second common theme is reaction with a proton or other Lewis acid to form a resonancestabilized cation-– protonation increases the electron deficiency of the carbonyl carbon and makes it more reactive toward nucleophiles R R f ast C O + H-B R B+ + R R O-H COH R C OH + B - R + H-Nu + R C OH + s low Nu C + H-B R R Tetrah edral carbonyl addition compoun d 24 Organic Organic Lecture Series – often the tetrahedral product of addition to a carbonyl is a new chiral center – if none of the starting materials is chiral and the reaction takes place in an achiral environment, then enantiomers will be formed as a racemic mixture Ap p roac h f ro m the top face Nu O Nu R R R' CO R' A pproach from the bottom face R' + Nu OH H3 O+ R R' + R O R' R OH Nu A n ew chiral ce n te r i s cre ate d Nu A racemic mixture 25 Organic Lecture Series Addition of C Nucleophiles Addition of carbon nucleophiles is one of the most important types of nucleophilic additions to a C=O group – a new carbon-carbon bond is formed in the carbonprocess process – Focus on addition of these carbon nucleophiles: RLi RC C An organolithium An alkyne reagent anion - RMgX A Grignard reagent CN Cyanide ion 26 Organic Organic Lecture Series Grignard Reagents • Given the difference in electronegativity between carbon and magnesium (2.5 1.3), the C-Mg bond is polar covalent, with Cδ- and Mgδ+ – in its reactions, a Grignard reagent behaves as as a carbanion • Carbanion: an anion in which carbon has an unshared pair of electrons and bears a negative charge – a carbanion is a good nucleophile and adds to the carbonyl group of aldehydes and ketones 27 Organic Lecture Series Grignard Reagents – addition of a Grignard reagent to formaldehyde followed by H3O+ gives a 1° alcohol O CH 3 CH2 - Mg Br + H- C- H ether Formaldehyde O [ MgBr] CH3 CH2 -CH2 A magn esium alkoxide + HCl H2 O OH 2+ CH3 CH2 -CH2 + Mg 1-Prop anol (a 1° alcoh ol) 28 Organic Organic Lecture Series Grignard Reagents – addition to any other RCHO gives a 2°alcohol MgBr O + ether H Ac e tal de hy de (an ald ehyde) O [ MgBr] + OH HCl H2 O + Mg2 + A magn esiu m alk oxid e 1-Cycloh exyleth anol (a 2° alcohol; (racemic) 29 Organic Lecture Series Grignard Reagents – addition to a ketone gives a 3°alcohol O Ph-MgBr Ph e ny l magnesiu m b romide + Ac e ton e (a ketone) O [ MgBr] Ph A magnes ium alk oxid e + eth er HCl H2 O OH + Mg 2+ Ph 2-Phenyl-2-propanol (a 3° alcohol) 30 ...
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This note was uploaded on 10/10/2010 for the course CH 57689 taught by Professor Goddard during the Spring '10 term at University of Texas.

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