Structural+isomers

Therefore isomers can have different physical properties or even chemical properties. Eg: Isomers of butane As you can see, both isomers have the same molecular formula that is C 4 H 10  but different structural formulas, that is, the atoms are arranged differently in the molecule in each case. // In a full structural formula every bond and every atom needs to be included. If the hydrogen atoms are omitted, it is called a skeletal structure. Eg: // 
 * Structural isomers **are compounds that have the same molecular formula but have different arrangements of atoms in the molecule. (have different structural formula)
 * [[image:butane_isomer_1.png]] || [[image:butane_isomer_2.png]] ||
 * // Extra: //**

__**// Note that a skeletal structure is not accepted in an IB examination. //**__

The IUPAC (international union of pure and applied chemists) system is usually used to name organic compounds. A compound is considered to consist of a hydrocarbon backbone to which side chains and functional groups are attached. Usually a backbone is considered to be the longest, continuous chain of carbon atoms in the molecule which gives the stem of the compounds’ name. These names would change as follows if a hydrogen atom is removed from the chain.
 * No of carbon atoms || stem ||
 * 1 || meth ||
 * <span style="display: block; font-family: Tahoma,sans-serif; font-size: 14pt; text-align: center;">2 || <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Eth ||
 * <span style="display: block; font-family: Tahoma,sans-serif; font-size: 14pt; text-align: center;">3 || <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Prop ||
 * <span style="display: block; font-family: Tahoma,sans-serif; font-size: 14pt; text-align: center;">4 || <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">But ||
 * <span style="display: block; font-family: Tahoma,sans-serif; font-size: 14pt; text-align: center;">5 || <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Pent ||
 * <span style="display: block; font-family: Tahoma,sans-serif; font-size: 14pt; text-align: center;">6 || <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Hex ||

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">If one Hydrogen is removed from the chain:
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Containing **1 carbon** atom the name changes to meth yl
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Containing **2 carbon** atoms the name changes to eth y <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">l
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Containing **3 carbon** atoms the name changes to prop y <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">l
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Containing **4 carbon** atoms the name changes to but yl
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Containing **5 carbon** atoms the name changes to pent yl
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Containing **6 carbon** atoms the name changes to hex yl

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">According to the naming system, the backbone is named and then you look for the side chains and in order to give the location of a side chain you have to say on which carbon it is attached to. Therefore you count the carbon atoms from both ends and use the number that is the smallest.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Eg1:

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">4 carbons in a chain so its stem is butane, with side group being methyl. Count from left and right (you get 2 & 3) so we take 2 as the position of the methyl group. Therefore, the name is **2-methyl butane**.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">eg2: <span style="font-family: Tahoma,sans-serif; font-size: 14pt;"> <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The compound is called **2,2-dimethylpropane.** <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">the number **2** shows the //position of// each side chain. <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**di** shows that there are //2 side chains//. <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**Methyl** is the //name of// each //side chain//. <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**Propane** is the name of the //longest (main) chain//.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The prefix cycle can be added to a name to show that the carbon atoms are arranged in a chain.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Different structural isomers of a compound have different physical properties (different boiling points) <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Usually isomers which are more spherical have lower boiling points because the surface area is smaller for forming intermolecular forces of attraction which thus results in lower boiling points.

By the end of this lesson you should be able to: __** Next up- Alkanes **__
 * Describe what structural isomers are.
 * Deduce the structural formula of isomers of alkanes with upto 6 carbons in the chain
 * Use the IUPAC naming system for naming isomers
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