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Ofun02 - Compound Structure Carbonyl Fundamentals(All...

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Table Note: Imines are not included in this table however they have similar chemistry to aldehydes because the functional groups share many similarities. Both contain a pi bond between a carbon and heteroatom. In addition both can undergo the three fates: nucelophilic attach, electrophilic attach, and enolate formation. Table Diagrams: www.wikipedia.org Carbonyl Fundamentals (All information and examples borrowed from Chem. 14D Thinkbook for Fall 2006, Dr. Hardinger’s Lecture Recordings and Paula Yurkanis Bruce’s Organic Chemistry 4 th edition, unless otherwise indicated) Carbonyl - the functional group is comprised of a carbon atom double-bonded to an oxygen atom (C=O). The various types of carbonyl containing functional groups are listed in the table on the right. Carbonyls can function as both a nucleophile and an electrophile. The polarity of the carbon-oxygen bond causes there to be a partial positive charge on the carbon atom and a partial negative charge on the oxygen atom. This electron-deficient carbon atom acts as an electrophile. The carbonyl group can also act as a nucleophile. The oxygen of this functional group is electron rich because of its lone pairs and the pi bond. Nucleophilic attack on another molecule by the lone pairs on oxygen or by the pi bond give the same result because the products are resonance structures and thus identical. Three C=O Fates Accept nucleophile at carbon Occurs in ALL Carbonyl addition mechanisms Produces tetrahedral adduct which occurs when the carbonyl carbon goes from sp 2 to sp 3 hybridization. Depending on if there is a leaving group attached to the carbonyl carbon there are two possibilities for the product of a nucleophilic attack on the carbonyl carbon. o Addition: no leaving group (LG) present . Occurs with aldehydes and ketones since alkenes and hydrogen are not LGs. The first step involves nucleophilic attack on the partially positive carbon atom to create the tetrahedral adduct resulting in an oxygen with a formal positive charge. The oxygen is then protonated to create an alcohol. Compound Structure Aldehyde Ketone Carboxylic Acid Ester Amide Primary, Secondary, Tertiary (shown) Enone Acetyl Chloride Acetic Anhydride Diagram Taken From: http://www.chemhelper.com/nucadd.html
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o Nucleophilic Carbonyl Substitution: LG is present . Occurs with ester, amide, anhydride, and acid chloride functional groups. Accept electrophile (usually H+) at oxygen There are two possible sites for nucleophilic attack of the carbonyl on an electrophile: the lone pairs and the pi bond. Is there a preference for the electrophile (usually H+) to be accepted by the lone pair or the pi bond? No. Both sites are nucleophilic and both lead to the same product through resonance.
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