All About Alkenes

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IUPAC Names

IUPAC Names

To form the root of the IUPAC names for alkenes, simply change the -an- infix of the parent to -en-.  For example, CH3-CH3 is the alkane ethANe.  The name of CH2=CH2 is therefore ethENe.  In higher alkenes, where isomers exist that differ in location of the double bond, the following numbering system is used:

1. Number the longest carbon chain that contains the double bond in the direction that gives the carbon atoms of the double bond the lowest possible numbers.

2. Indicate the location of the double bond by the location of its first carbon.

3. Name branched or substituted alkenes in a manner similar to alkanes.

4. Number the carbon atoms, locate and name substituent groups, locate the double bond, and name the main chain.

Naming substituted hex-1-enes [edit] Cis-Trans notation Main article: Cis-trans isomerism In the specific case of disubstituted alkenes where the two carbons have one substituent each, Cis-trans notation may be used. If both substituents are on the same side of the bond, it is defined as (cis-). If the substituents are on either side of the bond, it is defined as (trans-).

The difference between cis- and trans- isomers [edit] E,Z notation Main article: E-Z notation When an alkene has more than one substituent (especially necessary with 3 or 4 substituents), the double bond geometry is described using the labels E and Z. These labels come from the German words “entgegen,” meaning “opposite,” and “zusammen,” meaning “together.” Alkenes with the higher priority groups (as determined by CIP rules) on the same side of the double bond have these groups together and are designated Z. Alkenes with the higher priority groups on opposite sides are designated E. A mnemonic to remember this: Z notation has the higher priority groups on “ze zame zide.” The difference between E and Z isomers [edit] Groups containing C=C double bonds IUPAC recognizes two names for hydrocarbon groups containing carbon-carbon double bonds, the vinyl group and the allyl group. .[2] AlkeneGroups.png

February 3, 2010 Posted by | IUPAC Nomenclature, Uncategorized | Leave a comment

Alkenes

Boiling Points

The boiling point of each alkene is very similar to that of the alkane with the same number of carbon atoms. Ethene, propene and the various butenes are gases at room temperature. All the rest that you are likely to come across are liquids.

In each case, the alkene has a boiling point which is a small number of degrees lower than the corresponding alkane. The only attractions involved are Van der Waals dispersion forces, and these depend on the shape of the molecule and the number of electrons it contains. Each alkene has 2 fewer electrons than the alkane with the same number of carbons.

Solubility

Alkenes are virtually insoluble in water, but dissolve in organic solvents.

February 1, 2010 Posted by | Uncategorized | Leave a comment

IUPAC NOMENCLATURE OF ALKENES

To name alkenes:

1. Find the longest chain containing the alkene

2. Number the chain, giving the double bond the lowest possible number.

3. For cycloalkenes, begin numbering at the double bond and proceed through the double bond in the direction to generate the lowest number at the first point of difference.

4. Assign stereochemistry using the E-Z designation

February 1, 2010 Posted by | Uncategorized | Leave a comment

Alkene Nomenclature

Alkenes represent one of the most common functional groups in organic chemistry. An alkene contains only carbon and hydrogen (a hydrocarbon) and contains at least one double bond (termed an unsaturated hydrocarbon). Alkenes have the general formula CnH2n, thus, an alkene with 10 carbons (n = 10) will have 2(10) = 20 hydrogens, or the molecular formula C10H20; each double bond therefore contributes one degree of unsaturation.

The root, or parent name for an unbranched alkene is taken directly from the number of carbons in the chain according to a scheme of nomenclature established by the International Union of Pure and Applied Chemistry (IUPAC), as described previously for alkanes.

To name alkenes:

1. Find the longest chain containing the alkene

The IUPAC name for an alkene is constructed of two parts: 1) a prefix (meth… eth… prop…, etc.) which indicates the number of carbons in the main, or parent, chain of the molecule, and 2) the suffix …ene to indicate that the molecule is an alkane.

For branched-chain alkanes, the name of the parent hydrocarbon is taken from the longest continuous chain of carbon atoms containing the double bond.

2. Number the chain, giving the double bond the lowest possible number.

Numbering of the carbons in the parent chain is always done in the direction that gives the lowest number to the double bond, or, the lowest number at the first point of difference. If there are different substituents at equivalent positions on the chain, the substituent of lower alphabetical order is given the lowest number.

If the same substituent occurs more than once in a molecule, the number of each carbon of the parent chain where the substituent occurs is given and a multiplier is used to indicate the total number of identical substituents; i.e., dimethyl… trimethyl… tetraethyl…, etc. In constructing the name, substituents are arranged in alphabetical order, without regard for multipliers.

3. For cycloalkenes, begin numbering at the double bond and proceed through the double bond in the direction to generate the lowest number at the first point of difference.

One of the most common mistakes in naming cycloalkenes is to generate the lowest number sequence around the ring, disregarding this rule. Once again, the numbering must begin at the double bond and proceed through the bond in the direction to generate the lowest number sequence.

4. Assign stereochemistry using the E-Z designation

Historically, alkenes have been named using cis- and trans- to represent stereochemistry around the double bond; cis- for compounds where the “main substituents” are on the same side of the double bond, and trans- when they are on opposite sides. This system clearly breaks down, however, in more complex molecules where decisions concerning the “main substituents” are not easily made, and the E-Z system provides a set of rules to aid in these decisions.

February 1, 2010 Posted by | Uncategorized | Leave a comment

Uses of alkenes

Alkenes are produced from the alkanes in crude oil by a process called cracking. Cracking uses heat and a catalyst to decompose alkanes. The cracking process is important because it turns less useful alkanes into more useful smaller ones and produces very useful alkenes like ethene, the starting material for many plastics.

catalyst: A substance which speeds up a chemical reaction without being altered or consumed in the process itself.

Alkenes are unsaturated hydrocarbons with one double bond (R-C=C-R). They are from a homologous series with the general formula CnH2n. The 1st member to possess this functional group is ethane, C2H4. Ethene is an important raw material for the petrochemical industry. In fact, more commercial chemicals are produced from Ethene than from any other hydrocarbon intermediate. This unique position of ethene is due to favorable inherent properties as summarized below :

i. Simple but reactive structure
ii. Inexpensive
iii. Easily available through cracking of hydrocarbons

Alkenes are much more reactive than alkanes because alkenes are unsaturated (they have a reactive double bond). An alkene may be distinguished from an alkane by shaking the hydrocarbon with bromine water. Bromine water is reddish-brown, and will decolourised with an alkene but not with an alkane. Bromine adds across the double bond of an alkene to form a colourless dibromo alkane. This is an example of an addition reaction. An addition reaction occurs when two or more reactants join together to form a single product.

Uses of alkenes

Alkenes are extremely important in the manufacture of plastics. All plastics are in some way related to alkenes. The names of some plastics (Polythene or Poly Ethene, Polypropene), relate to their alkene partners. Plastics are used for all kinds of tasks, from packaging and wrapping, to clothing and outdoor apparel.

Lower alkenes are used as fuel and illuminant. These may be obtained by the cracking of kerosene or petrol.

For the manufacture of a wide variety of polymers, e.g., polyethene, polyvinylchloride (PVC) and teflon etc.

As raw materials for the manufacture of industrial Chemicals such as alcohols, aldehydes, and etc.

Besides, alkenes also used for artificial ripening of fruits, as a general anesthetic, for making poisonous mustard gas (War gas) and ethylene-oxygen flame.

References :

1. GCSE Science

2. Chemistry Guide

3. Carbon Chemistry

January 31, 2010 Posted by | Uncategorized | Leave a comment

Alkene

Alkenes are unsaturated hydrocarbons with general formula; CnH2n and isomeric with cycloalkenes. Alkenes can be prepared from dehydration of alcohols and dehydrohalogenation of alkyl halide. To form the root of the IUPAC (International Union and Applied Chemistry ) names for alkenes, simply change the -an- infix of the parent to -en-. For example, CH3-CH3 is the alkane therefore ethene. The name of CH2=CH2 is therefore ethene. Alkenes are hydrocarbons with carbon-carbon double bonds. In contrast to the easy rotation of sigma bonds, pi bonds cannot be rotated. This rigidity gives rise to cis-trans isomerism, also called geometric isomerism. Heats of hydrogenation can be used to compare the stabilities of alkenes. In general, more highly substituted double bonds are more stable, and trans isomers are slightly more stable than cis. Therefore, most eliminations give the most highly substituted alkene as their major product (Saytzeff’s rule). Alkenes undergo mainly electrophilic addition. The major products determined using Markovnikov’s Rule and stability of carbocation.

January 28, 2010 Posted by | Uncategorized | Leave a comment

Alkenes:Reactivity of Alkenes

There are several ways of reactivity of alkenes occur.First is hydrogenation.This is a reaction  of alkenes with hydrogen in the presence of catalyst such as platinium,nickel and palladium.

Second is halogenation which is occur in two conditions.First condition is in inert solvent where alkenes reacts with chlorine or bromine in CH2Cl2 at room temperature and forming vicinal dihalides.The second condition is in aqueous solution which the last product is haloalcohol called  halohydrin.

Next is hydrohalogenation which is a reaction when hydrogen halides(HI,HBr,HCl and HF)add to double bonds of alkenes and forming haloalkenes.The addition of the hydrogen halides follow Markovnikov Rule.

January 27, 2010 Posted by | Reactivity Of Alkenes, Uncategorized | Leave a comment

IUPAC NOMENCLATURE

Alkenes: Nomenclature

Alkenes are normally named using the IUPAC system. The rules for alkenes are similar to those used for alkanes. The following rules summarize alkene nomenclature.

  1. Identify the longest continuous chain of carbon atoms that contains the carbon-carbon double bond. The parent name of the alkene comes from the IUPAC name for the alkane with the same number of carbon atoms, except the -ane ending is changed to -ene to signify the presence of a double bond. For example, if the longest continuous chain of carbon atoms containing a double bond has five carbon atoms, the compound is a pentene.
  2. Number the carbon atoms of the longest continuous chain, starting at the end closest to the double bond. Thus,

    is numbered from right to left, placing the double bond between the second and third carbon atoms of the chain. (Numbering the chain from left to right incorrectly places the double bond between the third and fourth carbons of the chain.)

  3. The position of the double bond is indicated by placing the lower of the pair of numbers assigned to the double-bonded carbon atoms in front of the name of the alkene. Thus, the compound shown in rule 2 is 2-pentene.
  4. The location and name of any substituent molecule or group is indicated. For example,

    is 5-chloro-2-hexene.

  5. Finally, if the correct three-dimensional relationship is known about the groups attached to the double-bonded carbons, the cis or trans conformation label may be assigned. Thus, the complete name of the compound in rule 4 (shown differently here)

    is cis-5-chloro-2-hexene.

Read more: http://www.cliffsnotes.com/study_guide/Alkenes-Nomenclature.topicArticleId-22667,articleId-22613.html#ixzz0drILjOkb

January 27, 2010 Posted by | Uncategorized | Leave a comment

Alkene

In organic chemistry, an alkene is an unsaturated chemical compound .

To form the root of the IUPAC names for alkenes, simply change the -an- infix of the parent to -en-. The simplest alkenes, with only one double bond and no other functional groups. The  general formula of alkene is  CnH2n.The physical properties of alkenes are comparable with those of alkanes and depends on molecular mass . Alkenes are relatively stable compounds, but are more reactive than alkanes due to the presence of a carbon-carbon pi-bond. The reaction of alkene are  hydrogenation halogenation and hydrohalogenation.

January 27, 2010 Posted by | Uncategorized | Leave a comment

Alkene..ITS INTERESTING!!

Alkene is actually a type of chemical that we are familiar with. Most of us do not even notice how familiar we are with alkenes. For example, benzene. It is a type of alkene, to be exact, cyclic alkene. Benzene is widely use in everyday life. Thus, this proves that we are actually familiar with alkene, but most of us just dont even bother to know about it. So, if you want to know more about it, click here to fill up your minds with some interesting facts of alkene.

January 27, 2010 Posted by | Uncategorized | Leave a comment