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.
www.tutorsglobe.com offers Overhead Variances homework help, assignment help, case study, writing homework help, online tutoring assistance by accounting tutors.
perception of light tutorial all along with the key concepts of human vision, defects of vision, short sightedness, long-sight, color vision and color blindness
Prokaryotic Cell Structure tutorial all along with the key concepts of Prokaryotic Cellular Components, Prokaryotic Cell Wall, Cytoplasmic Membrane, Nuclear Material, Cytosol, Ribosomes, Flagella, Bacterial chromosomes, Plasmids
switch on the t.v. and test the screen for clear vision and turn the antenna till clear vision is acquired.
www.tutorsglobe.com offers answering questions to methods of calculation of national income, economics assignment help - homework help by online tutors.
Theory and lecture notes of Structure of Data management system all along with the key concepts of structure of data management system, Dictionary, Data Base manager, Data Communications, Transaction Management. Tutorsglobe offers homework help, assignment help and tutor’s assistance on Structure of Data management system.
tutorsglobe.com cuttings assignment help-homework help by online artificial technique of vegetative propagation tutors
Activity Based Budgeting needs identification of activities of the organization, establishing the factors that cause costs, the cost drivers and then collecting the costs of the activities in cost pools.
tutorsglobe.com symptoms of hiv assignment help-homework help by online emerging viral infections in humans tutors
tutorsglobe.com spermatophytes assignment help-homework help by online biodiversity tutors
www.tutorsglobe.com offers free tutorials and concepts of games with mixed strategies, analytical method, graphical method, simplex method, get solved your problems by live tutors.
Manufacture of Sulphuric acid and Sulphates tutorial all along with the key concepts of Manufacture of Sulphuric Acid, Contact Process, Manufacture of Sulphates
www.tutorsglobe.com offers Deployment Diagrams homework help, assignment help, case study, writing homework help, online tutoring assistance by computer science tutors.
Phylum Arthropoda tutorial all along with the key concepts of Exoskeleton of arthropods, Categorization and features of Arthropoda and Features of Chelicerata
the transformer is one of the very much reliable items of electrical equipment, requiring comparatively little attention; yet frequently even the minimum of attention is not provided, they as well occasionally breakdown due to neglect.
1959131
Questions Asked
3689
Tutors
1483698
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!