Alkyne Synthesis
Alkyne synthesis refers to the process of creating alkynes, which are hydrocarbons containing carbon-carbon triple bonds. This can be achieved through various methods such as dehydrohalogenation of vicinal dihalides, elimination reactions of alkyl dihalides, and alkylation of acetylene. These methods allow for the formation of carbon-carbon triple bonds, expanding the range of organic compounds that can be synthesized.
3 Key excerpts on "Alkyne Synthesis"
eBook - ePub- Graham Patrick(Author)
- 2004(Publication Date)
- Taylor & Francis(Publisher)
...Synthesis of an alkene from a vicinal dibromide. Figure 2. Synthesis of an alkyne from an alkene. Alkynes Alkynes can be synthesized from alkenes through a two-step process which involves the electrophilic addition of bromine to form a vicinal dibromide (Section H3) then dehydrohalogenation with strong base (Figure 2). The second stage involves the loss of two molecules of hydrogen bromide and so two equivalents of base are required. H2 Properties of alkenes and alkynes Key Notes Structure Alkenes are planar with bond angles of 120°. The carbon atoms of the C=C bond are sp 2 hybridized and the double bond is made up of one σ bond and one π bond. Alkynes are linear with the triple bond carbons being sp hybridized. The triple bond is made up of one σ bond and two π bonds. C=C Bond The C=C bond is stronger and shorter than a C–C single bond. However, the two bonds making up the C=C bond are not of equal strength. The π bond is weaker than the σ bond. Bond rotation round a C=C bond is not possible and isomers are possible depending on the substituents present. The more substituents which are present on an alkene, the more stable the alkene is. C≡C Bond An alkyne triple bond is stronger than a C–C single bond or a C=C double bond. The two π bonds present in the triple bond are weaker and more reactive than the σ bond. Properties Alkenes and alkynes are nonpolar compounds which dissolve in nonpolar solvents and are very poorly soluble in water. They have low boiling points since only weak van der Waals interactions are possible between the molecules. Nucleophilicity Alkenes and alkynes act as nucleophiles and react with electrophiles by a reaction known as electrophilic addition. The nucleophilic centers are the multiple bonds which are areas of high electron density. Spectroscopic analysis of alkenes Alkenes show characteristic C=C stretching absorptions in their IR spectra. Absorptions due to C-H stretching and bending may also be identifiable...
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
...The simplest alkyne, ethyne (HC CH) with two carbon atoms and two hydrogens atoms, was discussed earlier (Fig. 13.6). The alkyne with three carbon atoms, propyne, has the molecular formula; HC C CH 3. Butyne, with four carbon atoms, has two structural isomers: 1-butyne (HC C CH 2 CH 3) and 2-butyne (CH 3 C C CH 3). Because the sp. hybridized carbon atoms have a linear geometry, there can be no cis- and trans-isomers in the alkynes. Notice that 1,3-butadiene will be a structural isomer of the butynes, as they will all have the same molecular formula: C 4 H 6. One group of hydrocarbons that are cousins to the alkanes is the cycloalkanes with the general formula of C n H 2 n. Cycloalkanes are monocyclic alkanes consisting of carbon and hydrogen atoms bonded with single bonds in a molecular structure containing a single ring. The ring structure is considered to be the alkane backbone, which can also include branched side chains off the ring. Since the carbon atoms are joined together in a ring structure, two hydrogen atoms are lost from the parent alkane. This gives them one site of unsaturation with the same general molecular formula as the alkenes. So, a cycloalkane is a structural isomer of the corresponding alkene with the same molecular formula. The cycloalkanes have similar chemical properties as the saturated alkanes but, since they have two less hydrogens than the alkanes, they are technically unsaturated hydrocarbons. Cycloalkanes are named in the same manner as the normal alkanes. The simple cycloalkanes containing three to six carbon atoms are shown in Fig. 13.9. The structures shown in Fig. 13.9 are given in bonding notation and do not represent the actual structures of the molecules, which are not flat but are puckered in an attempt to achieve the109.5 degrees bonding angles of sp 3 hybridized alkanes...
eBook - ePub- Gopinathan Anilkumar, Salim Saranya, Gopinathan Anilkumar, Salim Saranya(Authors)
- 2020(Publication Date)
- Wiley-VCH(Publisher)
...In 1906, Goldberg used Cu for the synthesis of N-aryl compounds via C–N coupling reactions [ 5 ]. The successful organic transformations along with the economical and viable nature of the Cu-based catalysts were very attractive to the scientific community, and hence Cu-based catalysts demonstrated their efficiency in various types of C—C and C—X (X = heteroatom) coupling reactions [ 6 ]. This chapter summarizes the recent advances in the Cu-catalyzed homocoupling reactions of terminal alkynes, aryls, and alkenyls to yield symmetrical 1,3-diynes, biaryls, and bi-alkenyl systems respectively. 4.2 Synthesis of 1,3-Diynes via Homocoupling Reactions 1,3-Diynes are found in several natural products obtained from plants, bacteria, fungi, marine sponges, and corals and also possess prominent biological activities such as antifungal, antibacterial, antitumor, anti-HIV, and pesticidal properties [ 7 ]. The conjugated nature of 1,3-diyne makes it an important scaffold for the formation of molecular box as high efficiency hosts in supramolecular chemistry [ 8 ]. Additionally, these structural units also play an important role in the design of advanced materials such as liquid crystals, conjugated polymers, molecular wires, or nonlinear optic materials [ 9 ]. Previously, homocoupling of terminal alkynes by different catalysts was reviewed comprehensively [3c, 10]. However, in view of their material chemistry and bio-importance, numerous improvements and modifications were introduced in the synthesis of symmetrical 1,3-diynes from the corresponding terminal alkynes and other substrates. This chapter briefly discusses the advancement in the area to date. 4.2.1 Synthesis of 1,3-Diynes with Homogeneous Cu Catalysis As mentioned in the introduction, Glaser first reported the synthesis of diphenyldiacetylene via air oxidation of Cu(I)phenylacetylide [ 3 ]. The report attracted considerable attention in the area of C–C coupling chemistry...
