CHEM 1405 Concept Review: An Introduction to Organic Chemistry

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Organic Chemistry:  The study of compounds whose molecules contain carbon.

Alkanes:  Compounds composed of only carbon and hydrogen which have only single bonds.

Carbon will almost always have 4 bonds.  This causes carbon atoms that contain only single bonds to have a tetrahedral shape.

 

Complete Structural Formula:  A representation of a compound that shows all of the atoms & bonds.

Condensed Structural Formula:  A representation of a compound that shows the atoms arranged in the order that they are connected.  Either no bonds or only carbon-carbon bonds are shown.

                                             

 

 

Cycloalkanes:  alkanes where the carbons are connected in a ring

Examples:  

 

 

 

Alkanes with substituents

Substituent:  A branch attached to a longer carbon chain.  Branches can occur on alkanes of 3 or more carbons.  Branches can be in many different positions on the longest carbon chain.

Structural Isomers:  Molecules that have the same molecular formula but different bonding arrangements.

 

 

Naming Organic Compounds

The IUPAC (International Union of Pure and Applied Chemistry) naming system involves naming compounds systematically according their characteristics, the most important of which are:

A.  The length of the longest carbon chain.

B.  Which functional group or groups are present in the molecule.

C.  The presence of any branches (substituents) off of the longest carbon chain.

 

The general format of naming is as follows:

 

          First Ten Straight-Chain Alkanes
                                           

                                      

Functional Group:  An arrangement of atoms within a molecule that is responsible for giving that molecule its characteristic reactivity and properties.  Functional groups are the centers of reactivity in an organic molecule.

(For more info on specific functional groups, see the handout Functional Groups available online or in the SLC)

 

 

Steps to Naming Alkanes with Substituents

Step 1.  Find the longest continuous chain of carbon atoms, and use the name of this chain (see table “First Ten Straight-Chain Alkanes” on previous page) as the base name.

Example:
	Base Name: Heptane

 

Step 2.  Number the carbon atoms in the longest chain, beginning with the end nearest to a substituent.

Example:

 

Step 3.  Name each substituent.

Example:

 

Step 4.  Indicate the name and location (the number of the carbon atom on the longest chain) of each substituent in the prefix, listing them in alphabetical order if there is more than one. Be sure to put a dash (-) between numbers and letters.

 

Step 4b.  When 2 or more substituents of the same kind are present in a molecule, put a location number for each one (separated by commas) and use the prefixes di-,tri-,tetra-,penta-, and so forth to indicate how many of that type of substituent are present followed by the name of the substituent.  (NOTE: Prefixes are ignored in determining the alphabetical order of the substituents.) 

Example:  4-ethyl-2,5-dimethylheptane

 

 

Combustion Reactions:  Rapid reactions that produce a flame.  Generally, they will usually involve a hydrocarbon (C_xH_y) reacting with oxygen (O₂) to produce water (H₂O) and carbon dioxide (CO₂).

General Form:     $C_xH_y+O_2\:\longrightarrow\:CO_2+H_2O$                 Example:    $C_3H_8\left(g\right)+5O_2\left(g\right)\:\longrightarrow\:3CO_2\left(g\right)+4H_2O\left(l\right)$

 

 

Steps to Naming Alkenes with Substituents

1.  Find the longest continuous chain of carbon atoms WITH the double bond carbons, and name the chain the same as an alkane chain EXCEPT that the ending needs to be changed from “–ane” to “–ene.”

Example:
	Base Name:  Hexene

 

2.  Number the carbon atoms in the longest chain with the double bond, starting with the end nearest to the functional group (which is the double bond in this case). Look at the numbers of the 2 carbons that are double bonded.  Put the lower number in front of the base name to indicate the location of the double bond.

Example:
	Base Name: 1-Hexene

 

3.  Write the name of each substituent.

Example:

 

4.  Complete the name of the compound by writing the name and location of each substituent in the prefix, listing them in alphabetical order if there is more than one. Be sure to put a dash (-) between numbers and letters and a comma between consecutive numbers.

Example:  2,3-diethyl-5-methyl-1-hexene

 

 

 

Cis vs. Trans Isomers

When a double bond is present in the middle of a carbon chain, if each of the double bond carbons has EXACTLY one H attached to it, the molecule will have a designation of either “cis-“ if the hydrogens are on the SAME side or “trans-“ if the hydrogens are on the OPPOSITE side.  See image below for clarification: