Structural formula of alkanes alkenes and alkynes pdf

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structural formula of alkanes alkenes and alkynes pdf

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Alkanes belong to the family of saturated hydrocarbons that is; they contain only sigma bond linkages between carbon and hydrogen. Alkynes are similar to alkenes, except they involve a triple bond between two carbons rather than a double bond.

Most reactions of organic compounds take place at or adjacent to a functional group. In order to establish a baseline of behavior against which these reactions may be ranked, we need to investigate the reactivity of compounds lacking any functional groups. Such compounds are necessarily hydrocarbons , made up of chains and rings of carbon atoms bonded to a full complement of hydrogen atoms all carbons are sp 3 hybridized.

Naming Alkanes Alkenes And Alkynes Quiz With Answers

The largest database 1 of organic compounds lists about 10 million substances, which include compounds originating from living organisms and those synthesized by chemists. The number of potential organic compounds has been estimated 2 at 10 60 —an astronomically high number. The existence of so many organic molecules is a consequence of the ability of carbon atoms to form up to four strong bonds to other carbon atoms, resulting in chains and rings of many different sizes, shapes, and complexities.

The simplest organic compounds contain only the elements carbon and hydrogen, and are called hydrocarbons. Even though they are composed of only two types of atoms, there is a wide variety of hydrocarbons because they may consist of varying lengths of chains, branched chains, and rings of carbon atoms, or combinations of these structures. In addition, hydrocarbons may differ in the types of carbon-carbon bonds present in their molecules. Many hydrocarbons are found in plants, animals, and their fossils; other hydrocarbons have been prepared in the laboratory.

We use hydrocarbons every day, mainly as fuels, such as natural gas, acetylene, propane, butane, and the principal components of gasoline, diesel fuel, and heating oil. The familiar plastics polyethylene, polypropylene, and polystyrene are also hydrocarbons.

We can distinguish several types of hydrocarbons by differences in the bonding between carbon atoms. This leads to differences in geometries and in the hybridization of the carbon orbitals. Alkanes , or saturated hydrocarbons , contain only single covalent bonds between carbon atoms. Each of the carbon atoms in an alkane has sp 3 hybrid orbitals and is bonded to four other atoms, each of which is either carbon or hydrogen.

Carbon chains are usually drawn as straight lines in Lewis structures, but one has to remember that Lewis structures are not intended to indicate the geometry of molecules. Notice that the carbon atoms in the structural models the ball-and-stick and space-filling models of the pentane molecule do not lie in a straight line. Because of the sp 3 hybridization, the bond angles in carbon chains are close to The structures of alkanes and other organic molecules may also be represented in a less detailed manner by condensed structural formulas or simply, condensed formulas.

Instead of the usual format for chemical formulas in which each element symbol appears just once, a condensed formula is written to suggest the bonding in the molecule. These formulas have the appearance of a Lewis structure from which most or all of the bond symbols have been removed.

A common method used by organic chemists to simplify the drawings of larger molecules is to use a skeletal structure also called a line-angle structure. In this type of structure, carbon atoms are not symbolized with a C, but represented by each end of a line or bend in a line. Hydrogen atoms are not drawn if they are attached to a carbon. Other atoms besides carbon and hydrogen are represented by their elemental symbols. Drawing Skeletal Structures Draw the skeletal structures for these two molecules:.

Each carbon atom is converted into the end of a line or the place where lines intersect. All hydrogen atoms attached to the carbon atoms are left out of the structure although we still need to recognize they are there :. Interpreting Skeletal Structures Identify the chemical formula of the molecule represented here:. There are eight places where lines intersect or end, meaning that there are eight carbon atoms in the molecule.

Since we know that carbon atoms tend to make four bonds, each carbon atom will have the number of hydrogen atoms that are required for four bonds. This compound contains 16 hydrogen atoms for a molecular formula of C 8 H The number of carbon atoms present in an alkane has no limit.

Greater numbers of atoms in the molecules will lead to stronger intermolecular attractions dispersion forces and correspondingly different physical properties of the molecules. Hydrocarbons with the same formula, including alkanes, can have different structures. For example, two alkanes have the formula C 4 H 10 : They are called n -butane and 2-methylpropane or isobutane , and have the following Lewis structures:.

The compounds n -butane and 2-methylpropane are structural isomers the term constitutional isomers is also commonly used. Constitutional isomers have the same molecular formula but different spatial arrangements of the atoms in their molecules. The n -butane molecule contains an unbranched chain , meaning that no carbon atom is bonded to more than two other carbon atoms. We use the term normal , or the prefix n , to refer to a chain of carbon atoms without branching.

The compound 2—methylpropane has a branched chain the carbon atom in the center of the Lewis structure is bonded to three other carbon atoms. Identifying isomers from Lewis structures is not as easy as it looks.

Lewis structures that look different may actually represent the same isomers. They are identical because each contains an unbranched chain of four carbon atoms. The International Union of Pure and Applied Chemistry IUPAC has devised a system of nomenclature that begins with the names of the alkanes and can be adjusted from there to account for more complicated structures.

The nomenclature for alkanes is based on two rules:. When more than one substituent is present, either on the same carbon atom or on different carbon atoms, the substituents are listed alphabetically. Because the carbon atom numbering begins at the end closest to a substituent, the longest chain of carbon atoms is numbered in such a way as to produce the lowest number for the substituents.

The ending -o replaces -ide at the end of the name of an electronegative substituent in ionic compounds, the negatively charged ion ends with -ide like chloride; in organic compounds, such atoms are treated as substituents and the -o ending is used.

The number of substituents of the same type is indicated by the prefixes di- two , tri- three , tetra- four , and so on for example, difluoro- indicates two fluoride substituents. The four-carbon chain is numbered from the end with the chlorine atom. This puts the substituents on positions 1 and 2 numbering from the other end would put the substituents on positions 3 and 4. Four carbon atoms means that the base name of this compound will be butane.

The bromine at position 2 will be described by adding 2-bromo-; this will come at the beginning of the name, since bromo- comes before chloro- alphabetically. The chlorine at position 1 will be described by adding 1-chloro-, resulting in the name of the molecule being 2-bromochlorobutane.

We call a substituent that contains one less hydrogen than the corresponding alkane an alkyl group. The name of an alkyl group is obtained by dropping the suffix -ane of the alkane name and adding -yl :. The open bonds in the methyl and ethyl groups indicate that these alkyl groups are bonded to another atom.

Naming Substituted Alkanes Name the molecule whose structure is shown here:. The longest carbon chain runs horizontally across the page and contains six carbon atoms this makes the base of the name hexane, but we will also need to incorporate the name of the branch. In this case, we want to number from right to left as shown by the red numbers so the branch is connected to carbon 3 imagine the numbers from left to right—this would put the branch on carbon 4, violating our rules.

The branch attached to position 3 of our chain contains two carbon atoms numbered in blue —so we take our name for two carbons eth- and attach -yl at the end to signify we are describing a branch. Putting all the pieces together, this molecule is 3-ethylhexane.

This diversity of possible alkyl groups can be identified in the following way: The four hydrogen atoms in a methane molecule are equivalent; they all have the same environment.

They are equivalent because each is bonded to a carbon atom the same carbon atom that is bonded to three hydrogen atoms. Removal of any one of the four hydrogen atoms from methane forms a methyl group. Likewise, the six hydrogen atoms in ethane are equivalent and removing any one of these hydrogen atoms produces an ethyl group.

Each of the six hydrogen atoms is bonded to a carbon atom that is bonded to two other hydrogen atoms and a carbon atom. However, in both propane and 2—methylpropane, there are hydrogen atoms in two different environments, distinguished by the adjacent atoms or groups of atoms:. Each of the six equivalent hydrogen atoms of the first type in propane and each of the nine equivalent hydrogen atoms of that type in 2-methylpropane all shown in black are bonded to a carbon atom that is bonded to only one other carbon atom.

The two purple hydrogen atoms in propane are of a second type. They differ from the six hydrogen atoms of the first type in that they are bonded to a carbon atom bonded to two other carbon atoms.

The green hydrogen atom in 2-methylpropane differs from the other nine hydrogen atoms in that molecule and from the purple hydrogen atoms in propane. The green hydrogen atom in 2-methylpropane is bonded to a carbon atom bonded to three other carbon atoms. Two different alkyl groups can be formed from each of these molecules, depending on which hydrogen atom is removed. Note that alkyl groups do not exist as stable independent entities. They are always a part of some larger molecule.

The location of an alkyl group on a hydrocarbon chain is indicated in the same way as any other substituent:. Alkanes are relatively stable molecules, but heat or light will activate reactions that involve the breaking of C—H or C—C single bonds. Combustion is one such reaction:. Alkanes burn in the presence of oxygen, a highly exothermic oxidation-reduction reaction that produces carbon dioxide and water. As a consequence, alkanes are excellent fuels.

For example, methane, CH 4 , is the principal component of natural gas. Butane, C 4 H 10 , used in camping stoves and lighters is an alkane.

Gasoline is a liquid mixture of continuous- and branched-chain alkanes, each containing from five to nine carbon atoms, plus various additives to improve its performance as a fuel. Kerosene, diesel oil, and fuel oil are primarily mixtures of alkanes with higher molecular masses. The main source of these liquid alkane fuels is crude oil, a complex mixture that is separated by fractional distillation.

You may recall that boiling point is a function of intermolecular interactions, which was discussed in the chapter on solutions and colloids. The vapors rise through bubble caps in a series of trays in the tower. As the vapors gradually cool, fractions of higher, then of lower, boiling points condense to liquids and are drawn off. No carbon-carbon bonds are broken in these reactions, and the hybridization of the carbon atoms does not change.

For example, the reaction between ethane and molecular chlorine depicted here is a substitution reaction:. The C—Cl portion of the chloroethane molecule is an example of a functional group , the part or moiety of a molecule that imparts a specific chemical reactivity. The types of functional groups present in an organic molecule are major determinants of its chemical properties and are used as a means of classifying organic compounds as detailed in the remaining sections of this chapter.

Organic compounds that contain one or more double or triple bonds between carbon atoms are described as unsaturated. You have likely heard of unsaturated fats. These are complex organic molecules with long chains of carbon atoms, which contain at least one double bond between carbon atoms. Unsaturated hydrocarbon molecules that contain one or more double bonds are called alkenes.

Double and triple bonds give rise to a different geometry around the carbon atom that participates in them, leading to important differences in molecular shape and properties. The differing geometries are responsible for the different properties of unsaturated versus saturated fats.

Ethene, C 2 H 4 , is the simplest alkene.

22.2: Alkanes, Cycloalkanes, Alkenes, Alkynes, and Aromatics

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Alkanes, Alkenes, and Acetylenes

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CHE 120 - Introduction to Organic Chemistry - Textbook

The largest database 1 of organic compounds lists about 10 million substances, which include compounds originating from living organisms and those synthesized by chemists. The number of potential organic compounds has been estimated 2 at 10 60 —an astronomically high number.

Unsaturated Hydrocarbons

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COMMENT 2

  • In chemistry , an alkene is a hydrocarbon that contains a carbon —carbon double bond. Unitmasco - 18.03.2021 at 07:28
  • Aromatic hydrocarbons are defined by having 6-membered ring structures with Union of Pure and Applied Chemistry (IUPAC) names for alkynes parallel. Pbrown12345 - 25.03.2021 at 15:43

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