Quinuclidones are a class of

bicyclic In chemistry, a bicyclic molecule () is a molecule that features two joined rings. Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and camphor. A bicyclic compound can be carbocyclic (a ...

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

s with

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

C₇H₁₁NO with two structural isomers for the base skeleton 3-quinuclidone and 2-quinuclidone. 3-Quinuclidone (1-azabicyclo .2.2ctan-3-one) is an uneventful molecule that can be synthesized as the

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dig ...

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quanti ...

in a Dieckman condensation: 3-Quinuclidinone hydrochloride

Organic reduction of this compound gives the compound quinuclidine, structurally related to DABCO, which has one additional bridgehead nitrogen atom. The other isomer, 2-quinuclidone, appears equally uneventful, but in fact it has defied synthesis until 2006. The reason is that this molecule is very unstable because its

amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...

group has the

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent su ...

lone pair and the

carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containin ...

group not properly aligned, as may be expected for an amide, as a result of steric strain. This behaviour is predicted by

Bredt's Rule Bredt's rule is an empirical observation in organic chemistry that states that a double bond cannot be placed at the bridgehead of a bridged ring system, unless the rings are large enough. The rule is named after Julius Bredt, who first discussed ...

, and formal

group resembles in fact an

, as evidenced by the ease of salt formation. The

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

of the tetrafluoroborate

of 2-quinuclidone is a six-step affair starting from norcamphor the final step being an

azide In chemistry, azide is a linear, polyatomic anion with the formula and structure . It is the conjugate base of hydrazoic acid . Organic azides are organic compounds with the formula , containing the azide functional group. The dominant ...

ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bon ...

Schmidt reaction (38% yield): This compound rapidly reacts with water to the corresponding

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

with a chemical half-life of 15 seconds. X-ray diffraction shows pyramidalization on the nitrogen atom (59° compared to 0 for reference dimethylformamide) and torsion around the carbon-nitrogen bond to an extent of 91°. Attempts to prepare the free-base lead to uncontrolled

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

. It is, nevertheless, possible to estimate its basicity in an experiment in which amine pairs (the quinuclidonium salt and a reference amine such as diethylamine or indoline) are introduced into a

mass spectrometer Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is u ...

. The relative basicity is then revealed by collision-induced dissociation of the heterodimer. Further analysis via the extended kinetic method allows for the determination of the proton affinity and gas phase basicity of 2-quinuclidonium. This method has determined that quinuclidone ranks among secondary and tertiary amines in terms of proton affinity.''Synthesis of 2-Quinuclidonium by Eliminating Water: Experimental Quantification of the High Basicity of Extremely Twisted Amides'' Tony Ly, Michael Krout, Don K. Pham, Kousuke Tani, Brian M. Stoltz, and Ryan R. Julian J. Am. Chem. Soc.; 2007; 129(7) pp 1864 - 1865; (Communication) This high basicity is hypothesized to be due to the loss of electron delocalization when the amide bond is twisted—this causes misalignment of the pi orbitals, resulting in loss of electron resonance.

References

{{reflist Quinuclidines Lactams