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Nomenclature of Alkynes

Nomenclature of Alkynes

Alkynes are unsaturated hydrocarbons characterized by the presence of carbon-carbon triple bonds and have a general formula CnH2n-2. The nomenclature of alkynes follows a set of rules similar to alkanes and alkenes; however, alkynes bear the suffix "-yne" instead of "-ane" or "-ene." There are two approaches to naming alkynes:

Structure and Physical Properties of Alkynes

Structure and Physical Properties of Alkynes

Introduction:
In nature, compounds containing both carbon and hydrogen are known as "hydrocarbons". Aliphatic hydrocarbons are compounds whose molecules contain saturated single bonds (i.e., alkanes) or unsaturated double or triple bonds. Alkenes contain carbon–carbon double bonds and have a structural formula CnH2n. Unsaturated hydrocarbons containing carbon–carbon triple bonds are called "alkynes" and are structurally represented by the formula CnH2n-2.
The simplest alkyne is ethyne, or...

π Molecular Orbitals of 1,3-Butadiene

π Molecular Orbitals of 1,3-Butadiene

Conjugated dienes have lower heats of hydrogenation than cumulated and isolated dienes, making them more stable. The enhanced stabilization of conjugated systems can be understood from their π molecular orbitals.
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...

¹H NMR: Long-Range Coupling

¹H NMR: Long-Range Coupling

The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.

Acidity of 1-Alkynes

Acidity of 1-Alkynes

The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.

π Molecular Orbitals of the Allyl Cation and Anion

π Molecular Orbitals of the Allyl Cation and Anion

An allyl group is a three-carbon conjugated system where the sp³-hybridized allylic carbon is bonded to a CH=CH2 group via a single bond. Allyl anions can be obtained by treating propene with a strong base that can deprotonate methyl groups. Allyl cations are formed as intermediates during substitution reactions involving allylic halides. In both cases, the hybridization of the allylic carbon changes from sp3 to sp2, giving rise to a carbon chain with three sp2-hybridized carbons, each with an...

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Microscopic Visualization of Porous Nanographenes Synthesized through a Combination of Solution and On-Surface Chemistry

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Electron dynamics at polyacene/Au(111) interfaces.

C D Lindstrom¹, M Muntwiler, X-Y Zhu

¹University of Minnesota, Department of Chemistry, Minneapolis, Minnesota 55455, USA.

The Journal of Physical Chemistry. B

|June 15, 2007

Summary

Two-photon photoemission spectroscopy reveals image resonances at polyacene/Au(111) interfaces. Nonane adsorption modifies these resonances, affecting electron density, binding energy, and lifetime.

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Multiscale Sampling of a Heterogeneous Water/Metal Catalyst Interface using Density Functional Theory and Force-Field Molecular Dynamics

Published on: April 12, 2019

Area of Science:

Surface Science
Spectroscopy
Materials Chemistry

Background:

Understanding electronic properties of organic/metal interfaces is crucial for device applications.
Polyacenes offer tunable electronic structures for interface studies.

Purpose of the Study:

Investigate excited electronic structure and dynamics at polyacene/Au(111) interfaces.
Characterize image resonances and their behavior upon overlayer adsorption.

Main Methods:

Utilized two-photon photoemission (2PPE) spectroscopy.
Studied interfaces with benzene, naphthalene, anthracene, tetracene, and pentacene on Au(111).
Examined the effect of nonane overlayers on interface electronic states.

Main Results:

Observed image resonances with free-electron-like dispersions across all polyacenes.
Found similar binding energies and lifetimes for these resonances.
Nonane adsorption decreased binding energy by ~0.3 eV and increased lifetime to ~110 fs.
Image resonances were insensitive to polyacene molecular size.

Conclusions:

Unoccupied molecular orbitals are weakly coupled to metal states and image resonances.
Electronic properties are dominated by the interface rather than polyacene size.
Nonane overlayers significantly influence image resonance characteristics.