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Why are unsaturated hydrocarbons more reactive than saturated hydrocarbons?

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kumarvaibhav123 | Student, Grade 11 | Salutatorian

Posted January 10, 2012 at 2:23 AM via web

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Why are unsaturated hydrocarbons more reactive than saturated hydrocarbons?

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bandmanjoe | Middle School Teacher | (Level 1) Senior Educator

Posted January 10, 2012 at 2:52 AM (Answer #1)

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Hydrocarbons are compounds that consist of only the elements carbon and hydrogen in their molecular formula.  They are largely compounds found in petroleum deposits and represent the decayed remains of once-living plants and animals.  They are used widely in the energy industry in the production of various fuels such as gasoline, diesel fuel, and kerosene.

Hydrocarbons fit into two categories, saturated and unsaturated.  The "saturated" designation means the carbon atoms in the compound have as many hydrogen atoms as they are allowed.  Take the simplest hydrocarbon, methane, for example.  There is one carbon and four hydrogens, which is the maximum bonding for each of the carbon atom's four single electrons.  There is no room for anything else to attach to the carbon atom, so to get a reaction to take place, one must remove one of the hydrogens already present.

Unsaturated hydrocarbons, however, are hydrocarbons that have at least one or two double or triple bonds between the carbon atoms.  The double bond indicates a vacancy where two electrons could potentially bind to the carbon atom.  It is a simple matter to get the unsaturated hydrocarbon to "relax" the double bond in a chemical reaction, so that another element may bind to it.  Therefore, unsaturated hydrocarbons tend to be more reactive in nature than do saturated hydrocarbons.

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senioreeto | Student, Undergraduate | Valedictorian

Posted January 13, 2012 at 5:52 PM (Answer #2)

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unsaturated hydrocarbons contain multiple bonds which involve the ovelapping of pi-orbitals.since the electons in the pi-orbitals lie sbove the axis between two bonded atoms,so they are more exposed to the atteck of electrophiles(electron lovers).thats why they are very reactive. on the other hand,saturated hydrocarbons are the hydrocarbons that contain single bonds only(e.g. alkanes)which involve the overlapping of sigma-orbitals,since the electrons in the sigma-orbitals lie on the axis between the two bonded atoms and are strongly attracted,so they are less exposed towards the attack of electrophiles,for this reason,they are termed as saturated or less reactive hydrocarbons.
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immvp | eNotes Newbie

Posted March 2, 2013 at 9:34 PM (Answer #3)

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Fully saturated hydrocarbons are symmetrical; so they are non-polar.

C-H bonds are strong.

Unsaturated hydrocarbons have a C=C double bond that distorts the symmetry of the molecule; making unsaturated hydrocarbons polar.

 

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