Introduction to Alkylation of Enolate Anions
The reaction of alkyl halides with enolate anions shows the similar problem of competing SN2 and E2 reaction paths that was come across previous in the alkyl halide chapter. Because enolate anions are extremely strong bases, they will generally cause elimination when reacted with 2º and 3º-halides. Halides that are not capable of elimination and/or have improved SN2 reactivity are the best electrophilic reactants for this reason. Four instances of the C-alkylation of enolate anions in synthesis are shown in the diagram. The first two use the versatile strong base LDA that is the reagent of choice for mainly intermolecular alkylations of simple carbonyl compounds. The dichloro alkylating agent employed in reaction no.1 nicely demonstrates the high reactivity of allylic halides and the unreactive nature of vinylic halides in SN2 reactions.
The additive influence of carbonyl groups on alpha-hydrogen acidity is illustrated by reaction no.3. Here the two hydrogen atoms activated by both carbonyl groups are over 1010 times more acidic than the methyl hydrogens on the ends of the carbon chain. Certainly, they are adequately acidic (pKa = 9) to allow whole conversion to the enolate anion in aqueous or alcoholic solutions. As displayed (in blue color), the negative charge of the enolate anion is delocalized above both oxygen atoms and the central carbon. Oxygens are the hydrogen bonded to solvent molecules; therefore the kinetically favored SN2 reaction takes place at the carbon. The monoalkylated result displayed in the equation still has an acidic hydrogen on the central carbon and another alkyl group might be attached there by repeating this sequence. The last instance (reaction no.4) is an interesting case of intramolecular alkylation of an enolate anion. Because alkylation reactions are irreversible, if the reactive sites are in close proximity, it is probable to form small highly strained rings. Reversible bond-forming reactions like the aldol reaction cannot be used for this purpose. In this reaction, the use of aqueous base is also remarkable, in sight of the very low enolate anion concentration noted previous for such type of systems. It is the quick intramolecular nature of the alkylation that allows these unfavorable conditions to be employed.
The five-carbon chain of the dichloroketone can take several conformations, two of them are approximated in the preceding picture. Even though conformer II of the enolate anion could produce a stable five-membered ring by an intramolecular SN2 reaction, assuming correct orientation of the α and γ' carbon atoms, the concentration of this perfectly coiled structure will be very low. In this example O-alkylation of the enolate anion, rather than the C-alkylation is preferred from stereoelectronic arguments. Alternatively, conformations in which the α and γ-carbons are correctly aligned for three-membered ring formation are much more numerous, the result being that as quick as the enolate base is formed it goes through fast and irreversible cyclization. Ring closures to four, five, six and seven-membered are also probable by intramolecular enolate alkylation, as demonstrated by the following instance. Generally, five and six-membered rings are thermodynamically most stable, where three-membered ring formation is favored kinetically.
Qualified and Experienced Organic Chemistry Online Tutors at www.tutorsglobe.com
Tutors at the www.tutorsglobe.com take pledge to provide full satisfaction and assurance in Alkylation of Enolate Anions homework help via online tutoring. Students are getting Chemistry homework help services across the globe with 100% satisfaction by online tutors. We value all our service-users. We provide email based Alkylation of Enolate Anions homework help - assignment help. You can join us to ask queries 24x7 with live, experienced and qualified Chemistry online tutors specialized in Alkylation of Enolate Anions. Through Online Tutoring, you would be able to complete your homework or assignments at your home.
Latest technology based Organic Chemistry Online Tutoring Assistance
Tutors at the www.tutorsglobe.com are committed to provide the best quality online tutoring assistance for homework help and assignment help services. They use their experience, as they have solved thousands of the Alkylation of Enolate Anions assignments, which may help you to solve your complex Alkylation of Enolate Anions homework. You can find solutions for all the topics come under the Alkylation of Enolate Anions. The dedicated tutors provide eminence work on your Organic Chemistry homework help and devoted to provide K-12 level Chemistry to college level chemistry help before the deadline mentioned by the student. Alkylation of Enolate Anions homework help is available here for the students of school, college and university. TutorsGlobe assure for the best quality compliance to your homework. Compromise with quality is not in our dictionary. If we feel that we are not able to provide the homework help as per the deadline or given instruction by the student, we refund the money of the student without any delay.
tutorsglobe.com organ of corti assignment help-homework help by online ear tutors
Theory and lecture notes of One-Way Analysis of Variance all along with the key concepts of one-way analysis of variance, homework help, assignment help. Tutorsglobe offers homework help, assignment help and tutor’s assistance on One-Way Analysis of Variance.
www.tutorsglobe.com offers engineering homework help, engineering assignment help, engineering tutoring assistance, projects help with best qualified engineering tutors.
Theory and lecture notes of Mathematical Induction all along with the key concepts of Regions of a Circle, Principle of Mathematical Induction, Annotated illustration of Mathematical Induction and Pattern Recognition. Tutorsglobe offers homework help, assignment help and tutor’s assistance on Mathematical Induction.
Avail finest Cognitive Science Assignment Help service today and get authentic and plagiarism free solutions with amazing discounts.
rigid body dynamics i tutorial all along with the key concepts of Translational Motion of a Rigid Body, Rotational Motion of Rigid Body, General Motion, Moment of Inertia, Radius of Gyration, Dumbbell, Moments and Couples
Modern Art Assignment Help is an effectual means to score your desired grades without putting your hands in complex tasks.
a memory card (occasionally known as a flash memory card or a storage card) is a small storage medium employed to store data like pictures, text, audio and video, for use on small, portable devises.
tutorsglobe.com use of chromium assignment help-homework help by online occurrence and principles of extraction of chromium tutors
tutorsglobe.com nature of coordination compounds assignment help-homework help by online types of salts tutors
Electrolytic methods tutorial all along with the key concepts of Voltammetry, principle of Voltammetry, Types of Voltammetry, Linear sweep Voltammetry, Cyclic Voltammetry, Differential Pulse Voltammetry, Electrochemical Cell Set-Up and Amperometry
homologous series-functional groups and isomerism tutorial all along with the key concepts of organic compounds by functional groups, structural isomerism, geometric isomerism
www.tutorsglobe.com offers Relationship homework help, assignment help, case study, writing homework help, online tutoring assistance by computer science tutors.
tutorsglobe.com tissue transplantation assignment help-homework help by online immunology tutors
Historical Viewpoint tutorial all along with the key concepts of Histories of Cells Discoveries, Bridge between Life and Non-life, Protoplasmic Constituents and The Neuron Theory
1961075
Questions Asked
3689
Tutors
1491167
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!