Name: alkene bonding, properties, and uses
Uploaded: 2025-05-22T09:05:33.000Z
Duration: 2 min 47 s
Channel: JoVE

Alkenes, or olefins, represented by the general formula CnH2n, are hydrocarbons containing a carbon&#8211;carbon double bond. The cyclic analogs, enclosing a double bond in a ring, are called cycloalkenes.
Exemplified by the simplest alkene, ethylene, the carbon atoms across the double bond are sp2&#160;hybridized. Head-to-head overlap of hybrid orbitals forms a sigma bond, and sideways overlap of the two p orbitals leads to a &#960; bond, which, according to molecular orbital theory, has the electron density concentrated above and below the molecular plane.
Although a double bond between sp2&#160;carbons is significantly shorter and stronger than the single bond between sp3 carbons, a &#960; bond is weaker than a &#963; bond. This is indicated by the carbon&#8211;carbon double bond energy, which is not twice that of a single bond. The less effective overlap of participating orbitals and higher energy of 2p electrons compared to sp2&#160;accounts for the weaker &#960; bond.
Because sp2&#160;orbitals have more s character compared to sp3, the carbon&#8211;hydrogen bonds formed by sp2&#8211;s overlap in ethylene are shorter than those created by sp3&#8211;s&#160;overlap in ethane.
Likewise, in propylene, the carbon&#8211;carbon single bond resulting from sp2&#8211;sp3&#160;

structure and bonding of alkenes

Structure and Bonding of Alkenes

Olefins, which are unsaturated hydrocarbons containing one or more carbon&#8211;carbon double bonds, are broadly divided into alkenes and cycloalkenes. The general chemical formula of an alkene is CnH2n.
Doubly bonded carbons are sp2 hybridized and have a trigonal planar geometry. The double bond is composed of a &#963;&#160;bond formed by the overlap of hybrid orbitals and a &#960;&#160;bond produced by the lateral overlap of unhybridized 2p orbitals on both the carbons. Each carbon atom is bonded to two hydrogen atoms through sp2&#8211;s orbital overlap. As the unhybridized p electrons have higher energy than the electrons in the hybrid orbitals, the &#960; bond electrons generally have higher energy than the &#963; bond electrons. Therefore, electrophiles react preferentially with the &#960; bond electrons of alkenes.
Ethylene, propylene, and butylene exist as colorless gases. Alkenes containing 5 to 14 carbon atoms are liquids, and those containing 15 or more carbon atoms are solids. Alkenes, being effectively nonpolar, are insoluble in water but soluble in nonpolar solvents.
The boiling points of alkenes increase with the molecular mass&#160;as the intermolecular forces become stronger with the increasing size of the molecules.
Table 1: Physical Properties of Alkenes and Cycloalkenes
<table style="margin-left: auto; margin-right: auto;">
	<tbody style="border: 1px solid black;">
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Name</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#160;Structural Formula </td>
			<td style="color: black; border: 1px solid black; text-align: center;">mp (&#176;C)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#160;bp (&#176;C)</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Ethylene</td>
			<td style="color: black; border: 1px solid black; text-align: center;">CH2=CH2</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#8722;169</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#8722;104</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Propylene</td>
			<td style="color: black; border: 1px solid black; text-align: center;">CH3CH=CH2</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#8722;185</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#8722;47</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">1-Butene</td>
			<td style="color: black; border: 1px solid black; text-align: center;">CH3CH2CH=CH2</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#8722;185</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#8722;6</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">1-Pentene</td>
			<td style="color: black; border: 1px solid black; text-align: center;">CH3CH2CH2CH=CH2</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#8722;165</td>
			<td style="color: black; border: 1px solid black; text-align: center;">30</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Cyclopentene</td>
			<td style="color: black; border: 1px solid black; text-align: center;">C5H8</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#8722;135</td>
			<td style="color: black; border: 1px solid black; text-align: center;">44</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Cyclohexene</td>
			<td style="color: black; border: 1px solid black; text-align: center;">C6H10</td>
			<td style="color: black; border: 1px solid black; text-align: center;">&#8722;104</td>
			<td style="color: black; border: 1px solid black; text-align: center;">83</td>
		</tr>
	</tbody>
</table>
Alkenes occur abundantly in nature. For example, ethylene, the simplest alkene, is found in nature as a plant hormone that affects the ripening of fruits. Lycopene and carotenes are the polyenes responsible for the red, orange colors of fruits and vegetables, like tomatoes and carrots. Also, alkenes are the structural frames of various plant essential oils and insect pheromones.

Olefins, which are unsaturated hydrocarbons containing one or more carbon&#8211;carbon double bonds, are broadly divided into alkenes and cycloalkenes. ...

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Alkene Structure and Reactivity

KEY TERMS AND CONCEPTS

alkene bonding, properties, and uses

Alkenes are unsaturated hydrocarbons with one or more carbon-carbon double bonds. They are also called olefins, and they are broadly divided into alkenes and cycloalkenes. The general formula for an alkene is CnH2n.

The carbons in a double bond are sp2 hybridized. This gives each carbon a trigonal planar shape. The double bond has two parts: a sigma bond from overlap of hybrid orbitals and a pi bond from side-by-side overlap of unhybridized 2p orbitals. Each carbon also bonds to two hydrogen atoms through sp2-s orbital overlap.

The pi bond electrons are higher in energy than the sigma bond electrons. Because of this, electrophiles react preferentially with the pi bond electrons of alkenes. This bonding pattern helps explain why the double bond is the reactive part of the molecule.

Simple alkenes such as ethylene, propylene, and butylene are colorless gases. Alkenes with 5 to 14 carbon atoms are liquids, while those with 15 or more carbon atoms are solids. Alkenes are effectively nonpolar, so they do not dissolve in water. They do dissolve in nonpolar solvents, and their boiling points rise as molecular mass increases because intermolecular forces become stronger in larger molecules.

The physical properties of both alkenes and cycloalkenes are shown in the table. Ethylene, propylene, 1-butene, 1-pentene, cyclopentene, and cyclohexene all appear with their melting points and boiling points. These values show how chain length and ring structure relate to state and temperature behavior.

Alkenes also appear in nature. Ethylene, the simplest alkene, acts as a plant hormone that helps control fruit ripening. Lycopene and carotenes are polyenes that give tomatoes, carrots, and other fruits and vegetables their red and orange colors. Alkenes are also found in the structures of plant essential oils and insect pheromones.

Alkene Bonding, Properties, and Uses

regioselectivity of electrophilic additions to alkenes: markovnikov's rule

regioselectivity-electrophilic-additions-to-alkenes-markovnikov-s

Markovnikov Addition Paths in Alkenes

Markovnikov addition in alkenes explains why one product often forms in greater amount during hydrohalogenation. When an unsymmetrical alkene reacts, two haloalkane constitutional isomers are possible. In most cases, hydrogen adds to the vinylic carbon with more hydrogens, and the halide part adds to the more substituted carbon. This preference is called regioselectivity. Regioselective reactions favor bond formation at one site over another, so one constitutional isomer becomes the major...

Alkenes are unsaturated hydrocarbons with one or more carbon-carbon double bonds. They are also called olefins, and they are broadly divided into alkenes and cycloalkenes. The general formula for an alkene is CnH2n. The carbons in a double bond are sp2 hybridized. This gives each carbon a trigonal planar shape. The double bond has two parts: a sigma bond from overlap of hybrid orbitals and a pi bond from side-by-side overlap of unhybridized 2p orbitals. Each carbon also bonds to two hydrogen...

nomenclature of alkenes

IUPAC Rules for Alkene Naming

IUPAC rules for alkene naming show how to name carbon chains with a double bond. A simple alkene changes the alkane suffix -ane to -ene. The double bond must be part of the parent chain, which is the longest carbon chain that contains the maximum number of double bonds. The chain is numbered so the doubly bonded carbon atoms get the lowest possible numbers. The location of the double bond is given by the number of its first carbon atom. In branched alkenes, the double bond takes priority over...

degree of unsaturation

Counting Rings and Double Bonds in Molecules

Degree of unsaturation helps count rings and double bonds in an organic molecule. It is also called the index of hydrogen deficiency, or IHD. The idea is based on comparing a compound with the acyclic alkane that has the same number of carbon atoms. Each double bond or ring removes two hydrogen atoms compared with a saturated analog. That loss equals one degree of unsaturation. For hydrocarbons, the formula is U = (2C + 2 - H) / 2, where C is the number of carbon atoms and H is the number of...

isomerism in alkenes

Cis, Trans, and E/Z Alkene Forms

Alkene isomers can differ in both bond position and spatial arrangement. 1-butene and 2-butene are constitutional isomers because the double bond is in a different place. 2-butene also shows stereoisomerism, which means its atoms are connected the same way but arranged differently in space. In 2-butene, the two methyl groups can sit on the same side of the double bond or on opposite sides. When the methyl groups are on the same side, the compound is called cis-2-butene. When they are on...

relative stabilities of alkenes

Alkene Stability: Heat and Structure

Alkene stability depends on heats of hydrogenation and on the structure around the double bond. A lower heat of hydrogenation means the alkene is more stable. Three main factors help explain these differences: the number of substituents on the double-bond carbons, hyperconjugation, and double-bond stereochemistry. Substitution across the double bond has a strong effect on stability. An alkene with two smaller substituents is more stable than its isomer with one large substituent. For example,...

introduction to electrophilic addition reactions of alkenes

introduction-to-electrophilic-addition-reactions-of-alkenes

Alkene Addition Reactions and Redox Changes

Alkene addition reactions show how a carbon-carbon double bond reacts with electrophiles and changes during the process. A simple, unconjugated alkene has a double bond with high electron density, so it can act as a weak base or a nucleophile. Its filled π orbital, called the HOMO, can interact with the empty LUMO of an electrophile.

key terms and concepts

Explore alkene bonding, sp2 geometry, physical properties, and natural examples like ethylene, lycopene, and carotenes in a K12 science lesson.

Alkene Bonding, Properties, and Uses | JoVE K12

organic chemistry

JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Alkene Bonding, Properties, and Uses

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