How Do You Know Wherher or Not Molecule Is an Alkene
Naming Alkenes and Alkynes
Alkenes and alkynes are named similarly to alkanes, based on the longest chain that contains the double or triple bond.
Learning Objectives
Translate between the construction and the proper name of an alkene or alkyne chemical compound
Key Takeaways
Key Points
- Alkenes and alkynes are named by identifying the longest chain that contains the double or triple bond.
- The concatenation is numbered to minimize the numbers assigned to the double or triple bail.
- The suffix of the compound is "-ene" for an alkene or "-yne" for an alkyne.
Fundamental Terms
- Alkenes: An unsaturated hydrocarbon containing at least one carbon–carbon double bond.
- alkyne: An unsaturated hydrocarbon containing at to the lowest degree one carbon—carbon triple bond between two carbon atoms.
- stereoisomer: I of a set of the isomers of a compound that exhibits stereoisomerism.
Alkenes are hydrocarbons that comprise 1 or more double bonds, while alkynes comprise 1 or more than triple bonds. The naming conventions for these compounds are similar to those for alkanes.
Identifying and Numbering the Longest Chain
Alkene and alkyne compounds are named by identifying the longest carbon chain that contains both carbons of the double or triple bond. This longest chain is named by the alkane series series convention: "eth-" for two carbons; "prop-" for three carbons; "simply-" for four carbons; etc. The carbon courage is numbered from the end that yields the lowest positioning for the double or triple bond.
Calculation Substituents
Substituents are added to the proper name as prefixes to the longest chain. Rotation is restricted effectually the double bail, so prefixes tin can be added to differentiate stereoisomers. Cis or trans is used to betoken whether college priority substituents are located on the same or opposite sides of the bond. If the chemical compound is cyclic, this information is noted by adding the "cyclo-" prefix.
Changing the Suffix
Next, the position of the double or triple bond is indicated using the position of the carbon in the bond with the lower courage number, and the suffix for the compound is inverse to "-ene" for an alkene and "-yne" for an alkyne. For cycloalkenes, the carbons in the double bond are numbered equally positions one and two.
Naming hexene with different substituents: Examples of substituted hex-ane-enes. Recall that the 1 could go in front of the discussion hexene as well. For example, the heart molecule could be named as 4-methyl-1-hexene.
For multiple double or triple bonds, "di-," "tri-," or "tetra-" tin can exist added prior to the "-ene" or "-yne." In these cases, an extra "a" is appended to the end of the name of the alkyl chain, like in the instance of butadiene. For compounds containing both double and triple bonds, the "-ene" suffix precedes the "-yne," and the compound is numbered to minimize the bond positions.
Properties of Alkenes
Due to the presence of a double bond in their carbon skeletons, alkenes are more than reactive than their related alkanes.
Learning Objectives
Recognize the properties of alkenes relative to alkanes
Key Takeaways
Fundamental Points
- Alkenes are generally more reactive than their related alkanes due to the relative instability of the pi bond.
- The melting and boiling points of alkenes are dictated past the regularity with which they tin can pack and the surface area of interaction.
- Rotation is restricted around the double bond in alkenes, resulting in diastereoisomers with different substitution patterns effectually the double bond.
Key Terms
- diastereoisomer: A stereoisomer having multiple chiral centers; one cannot normally be superimposed on the mirror image of another.
Alkene Structures
Ethylene: A space-filling model of ethylene, the simplest alkene, showing its planar construction.
Alkenes comprise a double bond that is composed of one sigma and one pi bond between two carbon atoms. The sigma bond has similar properties to those found in alkanes, while the pi bail is more reactive. The carbon atoms in the double bond are sptwo hybridized, forming a planar structure. Rotation around the double bond is disfavored, and so alkenes grade adequately stable isomers depending on the positioning of substituents on the same (cis) or contrary (trans) sides of the double bail. These isomers are called diastereoisomers.
Physical Properties of Alkenes
Thermal cracking: The factory of the Shukhov neat process past the great Russian engineer and scientist Vladimir Shukhov (1853-1939) in 1934. In petroleum geology and chemistry, thermal cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are cleaved down into simpler molecules such as calorie-free hydrocarbons, past the breaking of carbon-carbon bonds in the precursors.
The melting and humid points of alkenes are determined past the regularity of the packing, or the closeness, of these molecules. Alkene isomers that tin can achieve more regular packing have higher melting and boiling points than molecules with the same molecular formula but weaker dispersion forces. Alkenes are non-polar, and they are both immiscible in water and less dumbo than water. They are generally soluble in organic solvents. In addition, they do non deport electricity.
Reactivity of Alkenes
Alkenes are more reactive than their related alkanes due to the relative instability of the double bond. They are more probable to participate in a multifariousness of reactions, including combustion, addition, hydrogenation, and halogenation reactions. Alkenes can too be reacted, typically in the presence of a goad, to form polymers.
Applications
Large amounts of ethylene are produced from natural gas via thermal slap-up. Information technology is an important raw material for the synthesis of a number of plastics.
Reactions of Alkenes and Alkynes
Alkenes and alkynes are more reactive than alkanes due to their pi bonds.
Learning Objectives
Give examples of the various reactions that alkenes and alkynes undergo
Key Takeaways
Key Points
- Addition reactions involving alkenes and alkynes include hydrogenation, halogenation, and hydrohalogenation.
- Alkenes and alkynes are useful reagents in polymer synthesis—an important industrial awarding.
- Hydrogenation reactions typically apply a metal catalyst consisting of platinum, nickel, palladium, or rhodium.
Cardinal Terms
- Markovnikov's dominion: States that, with the addition of a protic acrid HX to an alkene, the acid hydrogen (H) becomes fastened to the carbon with fewer alkyl substituents, and the halide (10) grouping becomes attached to the carbon with more alkyl substituents.
- polymer: A long or larger molecule consisting of a chain or network of many repeating units; formed by chemically bonding together many identical or similar pocket-sized molecules called monomers.
Reactions of Alkenes and Alkynes
Alkenes and alkynes are more often than not more reactive than alkanes due to the electron density available in their pi bonds. In particular, these molecules tin participate in a diversity of addition reactions and can exist used in polymer formation.
Addition Reactions
Unsaturated hydrocarbons can participate in a number of dissimilar addition reactions across their double or triple bonds.
Addition reactions: Alkenes participate in a variety of add-on reactions.
These addition reactions include catalytic hydrogenation (addition of H2), halogenation (reaction with X2, where 10 is a element of group vii ), and hydrohalogenation (reaction with H-X, where X is a halogen), amongst others.
Cycloaddition
Alkenes undergo diverse cycloaddition reactions. Nigh notable is the Diels–Alder reaction with ane,three-dienes to requite cyclohexenes.
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Diels-Alder reaction: Here, the reaction of one,3-butadiene (the diene) reacts with ethylene (the dienophile) to produce cyclohexene.
This general reaction has been extensively developed, and electrophilic alkenes and alkynes are especially effective dienophiles. Cycloaddition processes involving alkynes are often catalyzed by metals.
Oxidation
Oxidation of alkynes past strong oxidizing agents such as potassium permanganate or ozone will yield a pair of carboxylic acids. The general reaction can be pictured as:
[latex]\text{RC}\equiv \text{CR}'\xrightarrow{\text{KMnO}_4} \text{RCO}_2\text{H}+\text{R}'\text{CO}_2\text{H}[/latex]
Past contrast, alkenes can be oxidized at low temperatures to form glycols. At college temperatures, the glycol volition further oxidize to yield a ketone and a carboxylic acrid:
[latex](\text{H}_3\text{C})_2\text{C}=\text{CHCH}_3\xrightarrow[\text{heat}]{\text{KMnO}_4}\text{H}_3\text{CCOCH}_3+\text{H}_3\text{CCO}_2\text{H}[/latex]
Here, we have 3-methyl-2-butene oxidizing to course acetone and acetic acid.
Hydrogenation
In the presence of a catalyst—typically platinum, palladium, nickel, or rhodium—hydrogen can be added across a triple or a double bond to have an alkyne to an alkene or an alkene to an methane series. In practice, it is difficult to isolate the alkene product of this reaction, though a poisoned catalyst—a catalyst with fewer available reactive sites—tin can exist used to practice then. Every bit the hydrogen is immobilized on the surface of the catalyst, the triple or double bonds are hydrogenated in a syn fashion; that is to say, the hydrogen atoms add to the aforementioned side of the molecule.
Halogenation
Alkenes and alkynes tin also be halogenated with the halogen adding across the double or triple bond, in a similar fashion to hydrogenation. The halogenation of an alkene results in a dihalogenated paraffin product, while the halogenation of an alkyne can produce a tetrahalogenated alkane.
Hydrohalogenation
Alkenes and alkynes can react with hydrogen halides like HCl and HBr. Hydrohalogenation gives the respective vinyl halides or alkyl dihalides, depending on the number of HX equivalents added. The addition of water to alkynes is a related reaction, except the initial enol intermediate converts to the ketone or aldehyde. If the alkene is disproportionate, the reaction will follow Markovnikov'southward rule—the halide will be added to the carbon with more alkyl substituents.
Markovnikov's rule: This rule dictates that the addition of a hydrogen halide (HX, in the instance of HBr) to an alkene volition pb to a production where the hydrogen is fastened to the carbon with fewer alkyl substituents, while the halide grouping is attached to the carbon with more alkyl substituents.
Hydration
Water tin be added beyond triple bonds in alkynes to yield aldehydes and ketones for terminal and internal alkynes, respectively. Hydration of alkenes via oxymercuration produces alcohols. This reaction takes identify during the treatment of alkenes with a strong acid as the goad.
Source: https://courses.lumenlearning.com/boundless-chemistry/chapter/alkenes-and-alkynes/
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