Chem 334 1st Edition Lecture 9Outline of Last Lecture I. Friedal Crafts alkylation and acylationOutline of Current Lecture II. Acid/Base Reactions with OrganometallicsIII. Organometalics and EpoxidesIV. Aldehydes and KetonesV. Nomenclature Current LectureAcid/Base Reactions:Organometallic compounds will function as either bases or nucleophiles. Organolithium (RLi) and organomagnesium (RMgX) are very strong bases. In the presence of weak acids, RLi and RMgX protonate, giving the hydrocarbon. MgI HO H O H3C-Li H-O-H CH4 OH- Li+In the reaction above, carbon takes any acidic hydrogen it can. Water (H2O) is therefore the acid in this reaction. You cannot form organometallics in the presence of an alcohol, NH, NHR, carboxylic acid, sulfonic acid, SH, or terminal alkyne.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. HMg/Et2O H OH How do we fix this problem with using alcohols? We use a protecting group. Essentially, we put a group on an alcohol to make it compatible with gringnards or organo meticalics: Silyl EtherSilyl Ether Formation:R-O-SiR3 Cl Si Br O SiNow we no longer have to worry about an acidic H groupOrganometalics and epoxides:An epoxide is an ether in a 3 membered ring. The carbons on the ring are sp3 hybridized and only have a 60⁰ angle between bonds. The ring is very strained, and therefore very reactive.R-MgBr R O H3O+ R OHBrO--OBrMgBrO–H OHBrOGood nucleophiles attack on less substituted side of the molecule and make alcohol.Electrophile: Formaldehyde: goes to be a primary alcoholH3C-MgI O O H3O OH Electrophile: aldehyde: goes to be a primary alcoholLI O O H3O OH HElectrophile: Ketone PictureBrMg O O H3O OH Ester(picture)H3C-MgI O O O H3O OH O OTertiary alcohols are more reactive towards nucleophiles than the esterAlways assume 2 equivalence of organometallic when doing reactions with esters because the ketone formed is much more reactive, and immediately starts to eat up the Grignard. Aldehydes and Ketones:Aldehydes are a carbonyl group bonded to an H atom and a carbon (excluding formaldehyde). Ketones are a carbonyl bonded to 2 carbons. Both aldehydes and ketones share several important physical properties. First of all, they are polar, with electrons being pulled up on to the oxygen and the lone pairs on the oxygen being basic. The nucleophile then always attacks at the carbon, since the carbon is less electronegative. They also have increased boiling points (compared to other atoms of same molecular weight) due to dipole-dipole interactions. Hydrogen bonding increases boiling point further.Nomenclature: The first part of aldehyde and ketone nomenclature is finding the longest carbon chain that contains the carbonyl. For an aldehyde, change the suffix from -e to –al. For a ketone, change suffix from –e to –one. When numbering, the aldehyde must be at the end of the chain. This means no number is needed to describe the position of the aldehyde(because it’s at the 1 position). For a ketone, the carbonyl gets the H H Hlowest number. For double bonded molecules, add en before the suffix. For triple bonds, add yn before the suffixExample:3-methyl butanal 2-heptanone O H 2-butenal 3-hexynoal O H
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