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Properties

Alkyl lithium compounds are either low melting solids or liquids, and often with high volatility (depending on the substituent) due to the covalent nature of the bonding. They are soluble in aliphatics, aromatics, and ethers. However, while the reaction with ethers is generally slow, [link] , alkyl lithium compounds can polymerize tetrahydrofuran (THF).

Organolithium compounds react rapidly with air and water (both vapor and liquid). The reaction with water is the basis of the Gillman double titration method for determining the concentration of organolithium reagents in solution.

Structure

The structure of organolithium compounds is dominated by their highly oligomeric nature as a result of 3-center 2-electron bridging bonds. In all cases the extent of oligomerization is dependant on the identity of the alkyl (or aryl) group. The alkyl-bridged bond is similar to those found for beryllium and aluminum compounds.

In the vapor phase any particular organolithium derivative show a range of oligomeric structures. For example, the mass spectrum of EtLi shows ions associated with both tetramers (e.g., [Et 3 Li 4 ] + ) and hexamers (e.g., [Et 5 Li 6 ] + ). The structures of the different oligomers have been predicted by molecular orbital calculations ( [link] ).

Proposed vapor phase structures for various oligomers of RLi.

Solution molecular weight measurements indicate the oligomerization is present (in the absence of a coordinating ligand such as Et 2 O or an amine). The extent of oligomerization depends on the steric bulk of the alkyl group ( [link] ). Oligomerization and solution structures have also been investigated by 7 Li and 13 C NMR spectroscopy.

Extent of oligomerization (n) for organolithium compounds [RLi] n in benzene solution.
R [RLi] n R [RLi] n
Me 4 Et 6
n Bu 6 t Bu 4

There are a large number of X-ray crystallographically determined structures for organolithium derivatives. The archetypal example is MeLi, which exists as a tetramer in the solid state ( [link] ). The lithium atoms are arranged as a tetrahedron and the carbon atoms are positioned on the center of the facial planes, i.e., the carbon is equidistant from each of the lithium atoms. In contrast, EtLi has a similar tetrahedral structure, but the α-carbon of the ethyl groups are asymmetrically arranged such that it is closer to one lithium atom than the other two.

Solid state structure of MeLi. Copyright: Ben Mills (2007).

It is possible to prepare monomeric organolithium compounds by the addition of amines, especially chelate ligands such as ethylenediamine (en) and tetramethylethylenediamine (TMED). The reactivity of RLi is increased dramatically by the addition of such Lewis bases. For example, PhCH 2 Li shows an increased reactivity of 10 4 with the addition of TMED.

The bonding in organolithium compounds is difficult to describe:

  • Based upon the relative electronegativity of Li (0.98) and C (2.5) it would be expected to have significant ionic character.
  • Organolithium compounds form electron deficient oligomers typical of covalent bonding and clearly not as a result of ionic aggregation.
  • The spin-spin coupling, J (C-Li), observed by NMR spectroscopy (10 – 15 Hz) are consistent with a covalent bond.
  • Organolithium compounds undergo radical reactions.

However, the overall description of the bonding in RLi is that of a covalent interaction with significant polar (ionic) character, i.e., M δ + -C δ - .

The use of organolithium compounds in organic synthesis

Organolithium compounds perform many of the reactions commonly observed for Grignard reagents. However, lithium reagents are generally more reactive than their Grignard analogs.

Hydrolysis

Organolithium compounds react with water to give the hydrocarbon and lithium hydroxide, [link] . Lithium alkyls also react with other hydroxylic compounds such as alcohols and carboxylic acids, [link] .

One important use of the hydrolysis reaction is specifically deuteration, [link] .

Reaction with carbonyls

Organolithium compounds react with organic carbonyls (aldehydes, ketones, and esters) to yield the alcohol on hydrolysis, [link] . This synthetic route is particularly useful since lithium reagents are far more reactive than the analogous Grignard, allowing reactions to be carried out at lower temperatures and minimizing enolization side reactions.

The high reactivity of alkyl lithium compounds means that they react with carboxylic acids to yield the ketone rather than the lithium carboxylate.

Organolithium compounds generally react with α,β-unsaturated ketones to give the 1,2-addition product, [link] . However, lithium dialkylcuprates, which are formed from the alkyl lithium and copper(I) iodide, [link] , add exclusively by the 1,4-addition, [link] .

Transmetallation

One of the most useful methods of preparing organometallic compounds is the exchange reaction of one organometallic compound with a salt of a different metal, [link] . This is an equilibrium process, whose equilibrium constant is defined by the reduction potential of both metals. In general the reaction will proceed so that the more electropositive metal will form the more ionic salt (usually chloride).

Lithium reagents may be used to prepare a wide range of organometallic compounds.

Bibliography

  • G. Graham, S. Richtsmeier, D. A. Dixon. J. Am. Chem. Soc. , 1980, 102 , 5759.
  • E. Weiss, E. A. C. Lucken, J. Organomet. Chem., 1964, 2 , 197.
  • H. O. House, Acc. Chem. Res., 1976, 9 , 59.

Questions & Answers

What is price elasticity of demand and its degrees. also explain factors determing price elasticity of demand?
Yutansh Reply
Price elasticity of demand (PED) is use to measure the degree of responsiveness of Quantity demanded for a given change on price of the good itself, certis paribus. The formula for PED = percentage change in quantity demanded/ percentage change in price of good A
GOH
its is necessarily negative due to the inverse relationship between price and Quantity demanded. since PED carries a negative sign most of the time, we will usually the absolute value of PED by dropping the negative sign.
GOH
PED > 1 means that the demand of the good is price elasticity and for a given increase in price there will be a more then proportionate decrease in quantity demanded.
GOH
PED < 1 means that the demand of the good is price inelasticity and for a given increase in price there will be a less then proportionate decrease in quantity demanded.
GOH
The factors that affects PES are: Avaliablilty of close substitutes, proportion of income spent on the good, Degree of necessity, Addiction and Time.
GOH
Calculate price elasticity of demand and comment on the shape of the demand curve of a good ,when its price rises by 20 percentage, quantity demanded falls from 150 units to 120 units.
Helen Reply
5 %fall in price of good x leads to a 10 % rise in its quantity demanded. A 20 % rise in price of good y leads to do a 10 % fall in its quantity demanded. calculate price elasticity of demand of good x and good y. Out of the two goods which one is more elastic.
Helen
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Grace Reply
labor is any physical or mental effort that helps in the production of goods and services
Kwabena
what is profit maximizing level of out put for above hypothetical firm TC = Q3 - 21Q2 + 600 + 1800 P = 600 MC = 3Q2 - 42Q + 600
Sosna Reply
consider two goods X and Y. When the price of Y changes from 10 to 20. The quantity demanded of X changes from 40 to 35. Calculate cross elasticity of demand for X.
Sosna
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Sosna
consider two goods X and Y. When the price of Y changes from 10 to 20. The quantity demanded of X changes from 40 to 35. Calculate cross elasticity of demand for X.
Sosna
The formula for calculation income elasticity of demand is the percent change in quantity demanded divided by the percent change in income.
Sosna
what is labor productivity
Lizzy Reply
if the demand function is q=25-4p+p² 1.find elasticity of demand at the point p=5?
Puja Reply
what are some of the difference between monopoly and perfect competition market
Obeng Reply
n a perfectly competitive market, price equals marginal cost and firms earn an economic profit of zero. In a monopoly, the price is set above marginal cost and the firm earns a positive economic profit. Perfect competition produces an equilibrium in which the price and quantity of a good is economic
Naima
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Obeng Reply
explicit cost is seen as a total experiences in the business or the salary (wages) that a firm pay to employee.
Idagu Reply
what is price elasticity
Fosua
...
krishna
it is the degree of responsiveness to a percentage change in the price of the commodity
Obeng
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John Reply
what is monopoly
Peter Reply
what is taxation
Peter
is the compulsory transfer of wealth from the private sector to the public sector
Jonna
why do monopoly make excess profit in both long run and short run
Adeola Reply
because monopoly have no competitor on the market and they are price makers,therefore,they can easily increase the princes and produce small quantity of goods but still consumers will still buy....
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Adeola Reply
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jimmy
investment is a money u used to the business
Mohamed
investment is the purchase of good that are not consumed today but are used in the future to create wealth.
Amina
investment is the good that are not consumed
Fosua
What is supply
Fosua
 Supply represents how much the market can offer.
Yusif
it is the quantity of commodity producers produces at the market
Obeng
what is the effect of scarce resources on producers
Phindu Reply
explain how government taxes and government producer subsidies affect supply
Chanda
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Charles Reply
what are the type of economic
Charles
macroeconomics,microeconomics,positive economics and negative economics
Gladys
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Gladys
process of production
Mutia
Basically factors of production are four (4) namely: 1. Entrepreneur 2. Capital 3. Labour and; 4. Land but there has been a new argument to include an addition one to the the numbers to 5 which is "Technology"
Elisha
what is land as a factor of production
Gladys
what is Economic
Abu
economics is how individuals bussiness and governments make the best decisions to get what they want and how these choices interact in the market
Nandisha
Economics as a social science, which studies human behaviour as a relationship between ends and scarce means, which have alternative uses.
Yhaar
Economics is a science which study human behaviour as a relationship between ends and scarce means
John
Economics is a social sciences which studies human behavior as a relationship between ends and scarce mean, which have alternative uses.....
Pintu
While the American heart association suggests that meditation might be used in conjunction with more traditional treatments as a way to manage hypertension
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waht is hydrating power of lithium carbonates
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Source:  OpenStax, Chemistry of the main group elements. OpenStax CNX. Aug 20, 2010 Download for free at http://cnx.org/content/col11124/1.25
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