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Topic: Carbocation

Related Topics

Nucleophile

Electrophile

Electrophilic substitution

Lewis base

Organolithium reagent

Lewis acid

George Andrew Olah

Iron(III) chloride

	Carbocation - Wikipedia, the free encyclopedia
		A carbocation is an ion with a positively-charged carbon atom.
		A carbocation in a chemical reaction is a reactive intermediate.
		Carbocations were also found to be involved in the SN1 reaction and E1 reaction and in rearrangement reactions such as the Whitmore 1,2 shift.
	en.wikipedia.org /wiki/Carbocation (514 words)

	SN1 reaction - Wikipedia, the free encyclopedia
		It involves a carbocation intermediate, and it is commonly seen in reactions of secondary or tertiary alkyl halides, or (under strongly acidic conditions) with secondary or tertiary alcohols.
		In addition bulky substituents on the central carbon increase the rate of carbocation formation because of the relief of steric strain that occurs.
		The resultant carbocation is also stabilized by both inductive stabilisation and hyperconjugation from attached alkyl groups, and the Hammond-Leffler postulate suggests that this too will increase the rate of carbocation formation.
	en.wikipedia.org /wiki/SN1_reaction (759 words)

	Carbocations (Organic chemistry) - Wikibooks, collection of open-content textbooks
		Carbocations are carbon atoms in an organic molecule bearing a positive formal charge.
		Clearly, the tertiary carbocation is the most stable, as it is surrounded by three other carbon atoms that share the burden of its positive charge.
		Carbocation intermediates are formed in three main types of reactions: additions to pi bonds, unimolecular eliminations, and unimolecular nucleophilic substitution.
	en.wikibooks.org /wiki/Carbocations_(Organic_chemistry) (445 words)

	The Very Best Books : Carbocation Chemistry
		Today s most authoritative and all-inclusive reference on the chemistry of carbocations A thorough understanding of reactive intermediates is at the heart of chemical transformations and thus, of modern chemistry.
		Carbocation Chemistry is a comprehensive, self-contained reference on this vital topic.
		Carbocation Chemistry assembles the most current information on this wide-ranging topic, and is an indispensable reference for academics and practitioners around the world and across the scientific spectrum.
	www.elise.com /store/0471284904/Carbocation_Chemistry.html (155 words)

	Use of deaminatively-generated carbocation as polymerization initiators - US Patent 6602967 (Site not responding. Last check: 2007-11-07)
		The carbocation is activated by thermal, photochemical or electron bombardment of a heterocyclic, aryl substituted or with an aryl ring fused sulfonium salt with a non-nucleophilic anion which causes the ring to open.
		Carbocations generally are formed from the heterolysis of some weak, polar bond in polar solvents in which the departure of a good leaving group and the formation of a reasonance and/or inductively stabilized cation are involved.
		Polymerization was successfully initiated with both a secondary carbocation intermediate in the styrene reaction and the less stable tertiary carbocation intermediate in the isobutylene reaction.
	www.patentstorm.us /patents/6602967.html (4405 words)

	Carbocations
		This is important because carbocations are formed as intermediates in may organic reactions; the specific involvement of carbocations in various reactions is covered in related pages.
		Carbocations are "hypovalent" species, inasmuch as they have only three shared pairs of electrons around carbon, instead of the usual four.
		Note that it is not the sigma bonds that are directly attached to the carbocation that is involved in hyperconjugation; these orbitals are perpendicular to the empty "p" orbitals, and as such, cannot overlap with it.
	www.personal.psu.edu /faculty/t/h/the1/carbocat.htm (1250 words)

	Messiah College: School of Health and Natural Sciences (Site not responding. Last check: 2007-11-07)
		Carbocations are classified by the number of carbon atoms covalently bonded to the charged carbon atom; three neighboring carbons make the carbocation tertiary (3°), two make it secondary (2°), one makes it primary (1˚).
		Stability of the carbocation decreases with the number of neighboring carbon atoms; therefore, a 3° carbocation is more stable than a 2° one.
		Carbocations are further destabilized when an electron withdrawing group (EWG) is located adjacent to the charge carrying carbon.
	www.messiah.edu /schools/health_nat_sci/Currier_Duane.html (578 words)

	Chloride ion catalyzed conformational inversion of carbocation intermediates in the hydrolysis of a benzo[a]pyrene ... (Site not responding. Last check: 2007-11-07)
		Chloride ion catalyzed conformational inversion of carbocation intermediates in the hydrolysis of a benzo[a]pyrene 7,8-diol 9,10-epoxide.
		The energy barrier for the inversion of these carbocation conformations must be large relative to the energy barriers for the reaction of each carbocation conformation with water.
		Yet, the cis/trans ratio of tetrols from the reaction of the carbocation intermediate from the hydrolysis of chlorohydrin 5 is different than the cis/trans tetrol ratio from the acid-catalyzed hydrolysis of diol epoxide 1, which hydrolyzes via a carbocation with the same connectivity as that formed in the hydrolysis of 5.
	www.pdg.cnb.uam.es /UniPub/iHOP/gp/9339719.html (266 words)

	Skill Development Exercises CA 17 D (Site not responding. Last check: 2007-11-07)
		The lower V.E. carbocation is lower in V.E. because it is a mixture of a 3
		Notice that in the example in the previous question, electrophilic attack of each double bond results in a different carbocation intermediate, and that one of these carbocation intermediates is lower in potential energy.
		The carbocation rearrangement is driven by the fact that the resulting carbocation is part of a large allyl system, whereas the starting carbocation is simply secondary.
	home.earthlink.net /~cuachemistry/organic/SDEAns/AnsSDE17D.htm (282 words)

	Carbocation Stability (Site not responding. Last check: 2007-11-07)
		Although generations of organic chemists have used rates of nucleophilic substitution reactions as a means of judging the stability of carbocations, this approach is fraught with error.
		Formation of carbocations in hyperacid media, the discovery of which won the Nobel for George Olah recently, allows us to study the properties of carbocations.
		C chemical shift of the carbocation carbon in hyperacid media, which is very nearly invariant with structure.
	chemistry.umeche.maine.edu /CHY556/carbocat.html (243 words)

	Carbon carbon double bonds (Site not responding. Last check: 2007-11-07)
		The carbocation is formed next to X. Resonance delocalisation is a recurring theme in chemistry and biochemistry.
		Although there is no formal carbocation formation (reaction stereospecific, no re-arrangement), the transition state must have partial carbocation character, this then will control the outcome of the reaction.
		A carbocation like transition state must exist, but it is not a fully fledged carbocation.
	speedy.st-and.ac.uk /~naismith/teaching/lectures/ch1004/topica2.htm (1298 words)

	Carbocation scavenging during oligonucleotide synthesis - US Patent 5510476 (Site not responding. Last check: 2007-11-07)
		The process of claim 1 wherein the carbocation scavenging agent is present in the acidic solution in the amount of from 1 to 10%.
		In preferred embodiments the carbocation scavenging agent is present in the deblocking solution in the amount of from 1 to 25%, with from 1 to 10% being especially preferred and more preferably from 4 to 6 percent.
		This is determined spectrophotometrically by quantitating the carbocation released at Amax 498 nm at acidic pH.
	www.patentstorm.us /patents/5510476.html (8831 words)

	carbocations (or carbonium ions)
		All carbocations (previously known as carbonium ions) carry a positive charge on a carbon atom.
		In a secondary (2°) carbocation, the carbon with the positive charge is attached to two other alkyl groups, which may be the same or different.
		In a tertiary (3°) carbocation, the positive carbon atom is attached to three alkyl groups, which may be any combination of same or different.
	www.chemguide.co.uk /mechanisms/eladd/carbonium.html (775 words)

	.: Research - Richard Research Group :.
		The most surprising and revealing result of these studies is that the rate constants for nucleophilic addition to α-substituted methoxybenzyl carbocations are largely independent of the α-substituents at the benzylic carbon.
		Many of the questions about carbocation reactivity addressed in this work have been answered, and many new questions have been raised so that this remains an area in which much exciting work is possible.
		One problem where considerable further progress is possibly concerns the characterization of the effect of sulfur bridging on the kinetic and thermodynamic stability of α-thioamide substituted carbocations.
	www.acsu.buffalo.edu /~jrichard/r_carbocations.html (487 words)

	ORGANIC CHEMISTRY I (Site not responding. Last check: 2007-11-07)
		The rate-determining step will thus be the formation of the carbocation, and since the leaving group, chloride, is the same for both compounds, the stability of the carbocation formed will determine the rate of reaction.
		The carbocation formed when the iodide falls off is planar (the C+ is sp2 hybridized), and can be attacked from either side by the nucleophile.
		Since the formation of the carbocation from the alkyl halide is an endothermic process, the more stable isomer of starting material will have a larger energy hill to climb to get to the same place, so it will react slower.
	www.muhlenberg.edu /depts/chemistry/COURSES/ORGANIC/RUSSELL/201/opa110904a.htm (1503 words)

	SparkNotes: Sn1E1 Reactions: Consequences of the Carbocation Intermediate (Site not responding. Last check: 2007-11-07)
		The carbocation intermediate ruins the stereospecificity of the reaction.
		Saytzeff's rule is founded on energetic stability, and thus is not affected by the random geometry introduced by the carbocation.
		Carbocations are most stable next to electron donating groups.
	www.sparknotes.com /chemistry/organic4/sn1e1/section2.rhtml (323 words)

	Rearrangement
		Rearrangement to a 2º-carbocation is favored by relief of small-ring strain in the case of pinene, and relief of steric congestion in the case of camphene.
		The chloride anion is located on one side of the carbocation formed by the alkyl shift, and immediately bonds to that face of the tricoordinate carbon.
		However, the carbocation resulting from a phenyl shift would be just as strained as its precursor; whereas the shift of a ring methylene group generates an unstrained cation stabilized by phenyl and oxygen substituents.
	www.cem.msu.edu /~reusch/VirtualText/rearrang.htm (7059 words)

	Encyclopedia: Carbocation (Site not responding. Last check: 2007-11-07)
		A Wagner-Meerwein rearrangement is a class of carbocation 1,2-rearrangement reactions in which a hydrogen, alkyl or aryl group migrates from one carbon to a neighbouring carbon.
		Organic chemistry is the scientific study of the structure, properties, composition, reactions, and synthesis of organic compounds that by definition contain carbon.
		It is obtained by removing a proton from benzene.
	www.nationmaster.com /encyclopedia/Carbocation (1417 words)

	Alkyl Halides Gen (Site not responding. Last check: 2007-11-07)
		For example, a 3° carbocation that is part of a three-membered ring is not as stable as an acyclic 3° carbocation because the cyclic carbocation has significant angle strain associated with it.
		carbon destroys its chirality and the carbocation is not chiral.
		Two distinct stereoisomers are generated: one from reaction of the nucleophile from the top side of the carbocation, and one from reaction of the nucleophile from the bottom side of the carbocation.
	acpcommunity.acp.edu /Facultystaff/brownewf/FEB_Web/Organic/Lab/Experiments/AlkylHalides/Alkyl_Halides_Gen.html (2430 words)

	Skill Development Exercises for Part A (Site not responding. Last check: 2007-11-07)
		The last carbocation would be expected to have the lowest potential energy because the + charge is spread out over five atoms.
		Construct an explanation for why the benzyl carbocation in the second row is lower in potential energy than the benzyl carbocation in the first row.
		The top benzyl carbocation has only secondary radical character (note the resonance structure shown), whereas the bottom benzyl carbocation has some tertiary radical character, demonstrated by the resonance structure shown.
	home.earthlink.net /~cuachemistry/organic/SDEAns/Ans13A.htm (534 words)

	Alkene Reactivity
		The carbocation intermediate formed in the first step of the addition reaction now assumes a key role, in that it directly influences the activation energy for this step.
		When an unsymmetrically substituted double bond is protonated, we expect the more stable carbocation intermediate to be formed faster than the less stable alternative, because the activation energy of the path to the former is the lower of the two possibilities.
		This supprising result may be explained by a carbocation rearrangement of the initially formed 2º-carbocation to a 3º-carbocation by a 1,2-shift of a methyl group.
	www.cem.msu.edu /~reusch/VirtualText/addene1.htm (3530 words)

	Wiley::Carbocation Chemistry
		A thorough understanding of reactive intermediates is at the heart of chemical transformations and thus, of modern chemistry.
		The study of carbocation chemistry has become one of the most fascinating and fruitful areas in organic chemistry.
		Carbocation Chemistry assembles the most current information on this wide-ranging topic, and is an indispensable reference for academics and practitioners around the world–and across the scientific spectrum.
	www.wiley.com /WileyCDA/WileyTitle/productCd-0471284904.html (286 words)

	[No title] (Site not responding. Last check: 2007-11-07)
		Tertiary carbocations are the most stable and form faster than secondary carbocations, which are more stable and form faster than primary carbocations.
		This general order is important because carbocations are very common intermediates and will be encountered frequently in our exploration of organic chemistry.
		Alkyl groups attached to the carbocation stabilize the positive charge by donating electron density to the positively charged carbon.
	people.uis.edu /gtram1/organic/alkenes/markovnikov.htm (422 words)

	Nucleophilic Substitution & Elimination
		In a tertiary carbocation, there are three carbon atoms, each bonded to three other atoms, connected to the electron deficient carbocation carbon.
		One outcome of this is that the carbocation intermediate "lives" long enough for a nucleophile to approach it on either face of the molecule.
		If the carbocation intermediate has the opportunity to engage in many collisions with potential nucleophiles, there is an equal chance that a nucleophile will attack at one lobe or the other of the p orbital.
	chemistry2.csudh.edu /rpendarvis/SN1Elim.html (2034 words)

	[No title] (Site not responding. Last check: 2007-11-07)
		The p-orbital that is not utilized in the hybrids is empty and is often shown bearing the positive charge since it represents the orbital available to accept electrons.
		As they have an incomplete octet, carbocations are excellent electrophiles and react readily with nucleophiles.
		Carbocations are prone to rearrangement via 1,2-hyride or 1,2-alkyl shifts if it generates a more stable carbocation
	www.mhhe.com /physsci/chemistry/carey/student/olc/graphics/carey04oc/ref/ch08carbocations.html (132 words)

	SN1 (Site not responding. Last check: 2007-11-07)
		A carbocation is formed in the slow step of an SN1 reaction.
		Attack of a nucleophile on the carbocation (SN1).
		Attack of a base on a H atom on a carbon atom adjacent to the carbocation (E1).
	people.uis.edu /gtram1/organic/alkylHalides/sn1.htm (351 words)

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