Goals for the Day Combustion Reactions of Alkanes

Goals for the Day: Combustion Reactions of Alkanes Functional Groups Naming Alkenes & Alkynes Physical Properties of Alkenes & Alkynes Reactions of Alkenes & Alkynes 1

Combustion of Alkanes contain single C—C bonds which are difficult to break. are the least reactive group of organic compounds. burn readily in the presence of oxygen. undergo combustion to produce carbon dioxide, water, and energy.

Combustion of Alkanes We use methane gas to cook food and heat homes. Propane gas is used in portable heaters and gas barbecues. Our cells get energy from the combustion of glucose.

Balancing a Combustion Equation Write the equation: Balance C: Balance H: Balance O with O 2:

Crude Oil/Fractional Distillation Hydrocarbons in crude oil are separated by their different boiling points in a process called fractional distillation which removes groups of hydrocarbons by continually heating the mixture to higher temperatures.

Crude Oil

Learning Check Propane gas is used to provide heat for cooking. Write a balanced

Step 1: What is the equation? Unbalanced equation: Propane has 3 carbons and therefore 2 n+2 hydrogens, or 8 hydrogens (or you can draw it out & count the # of hydrogens)

Step 2: Balance carbons… Unbalanced equation: Balance C:

Step Three: Balance Hydrogens Unbalanced equation: Balance C: Balance H:

Step 4: Balance oxygens… Unbalanced equation: Balance C: Balance H: Balance O:

Learning Check (You can work this one at home)… Write a balanced equation for the reaction for the complete combustion of heptane, C 7 H 16.

Solution Write a balanced equation for the reaction for the complete combustion of heptane, C 7 H 16. Balanced equation:

Elements in Organic Compounds In organic molecules, carbon atoms can form bonds with atoms

Functional Groups Functional groups are a characteristic feature of organic molecules that behave in a predictable way. are composed of an atom or a group of atoms. are groups that replace a H in the corresponding alkane. provide a way to classify families of organic compounds. 15

Alkenes and Alkynes Alkenes contain a double bond between adjacent carbon atoms. Alkynes contain a triple bond. Aromatic compounds contain a benzene ring. © 2013 Pearson Education, Inc. Chapter 12 Section 1 16

Alcohols, Thiols, and Ethers An alcohol contains the hydroxyl (–OH) functional group. Thiols contain a thiol (–SH) functional group. In an ether, an oxygen atom is bonded to two carbon atoms (– C–O–C–). Thiol 17

Aldehydes and Ketones An aldehyde contains a carbonyl group (C=O), which is a carbon atom with a double bond to an oxygen atom, attached to at least one hydrogen atom. In a ketone, the carbon of the carbonyl group is attached to two other carbon atoms. 18

Carboxylic Acids and Esters Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group. An ester contains the carboxyl group between carbon atoms. 19

Amines and Amides In an amine, the functional group is a nitrogen atom. In an amide, the hydroxyl group of a carboxylic acid is replaced by a nitrogen group. © 2013 Pearson Education, Inc. Chapter 12 Section 1 20

Learning Check Classify each of the following as alcohol, ether, aldehyde, ketone, carboxylic acid, ester, or amine. A. B. C. D. E. 21

Learning Check Classify each of the following as alcohol, ether, aldehyde, ketone, carboxylic acid, ester, or amine. A. alcohol B. ether C. amine D. E. carboxylic acid ester 22

Unsaturated Hydrocarbons Unsaturated hydrocarbons do not contain the maximum number of hydrogen atoms that could be attached to each carbon atom. are alkenes when they contain double C=C bonds. are alkynes when they contain triple C≡C bonds. react with hydrogen gas to form saturated hydrocarbons. Does anyone remember the bond angles?

Bond angles of alkenes & alkynes

Alkenes contain a carbon–carbon double bond that forms when adjacent carbon atoms share two pairs of valence electrons. are flat because the atoms in a double bond lie in the same plane. have a trigonal planar arrangement around the double bonded carbon atoms.

Ethene, or Ethylene has the chemical formula: C 2 H 4. has two carbon atoms connected by a double bond. has two H atoms bonded to each C atom. is flat with all the C and H atoms in the same plane. © 2013 Pearson Education, Inc. Chapter 12 Section 1 26

Alkynes have a triple bond that forms when two carbon atoms share three pairs of valence electrons. have a 180˚ angle and are linear.

Ethyne, or Acetylene has the chemical formula C 2 H 2 has a triple bond connecting the two carbon atoms. is used in welding (acetylene torches)…. A mixture of acetylene and oxygen undergoes combustion during the welding of metals.

Learning Check Identify each of the following compounds as an alkane, alkene, or alkyne. A. B. C. D.

Solution A. alkyne B. alkene C. alkene D. alkane

Poll: Where would we start numbering?

Try to draw…(hints are on the next slide if you need them)… 4 -isopropyl-4 -octene

One way to draw it… 4 -isopropyl-4 -octene

Cis and Trans Isomers Cis and trans isomers have the same formula, but different physical and chemical properties. occur because double bonds in alkenes are rigid and cannot rotate. We add the prefix cis or trans to denote whether the atoms bonded to the carbon atoms are on the same side or the opposite sides of the double bond.

Naming Cis–Trans Isomers The prefixes cis- or trans- are placed in front of the alkene name when there are cis–trans isomers. cis-1, 2 -Dibromoethene trans-1, 2 -Dibromoethene

Are these cis or trans?

Answers… Red = trans green = cis

Try to name this structure…

There are 6 carbons in the chain, so the base name is hexene… (hex for 6 carbons and ene since there is a double bond)

hexene We need two more things… A) a number for the position of the double bond B) cis or trans for the direction…

3 -hexene a number for the position of the double bond 3 cis or trans for the direction…remember to “draw a line through the double bond” since both “groups” are on the top of the green line, we use cis as the prefix

cis-3 -hexene

What would we name this?

This is trans-9 -methyl-3 -decene (note: we numbered from the left side since it is closest to the double bond)

Please draw cis-2 -pentene in your notebooks & I will check it…

Various possible structures… Note: this one is trans!

Try to draw trans-2 -heptene

Try to draw trans-2 -heptene Number of carbons in the chain = 7 Suffix = ene Where to draw the double bond in the chain? On carbon 2…

Last step is to check to make sure you have trans…make a line connecting the carbons of the double bond. The “groups” attached are on opposite sides of the line, so are trans!

Naming Cycloalkenes When naming a cycloalkene, if there are no substituents, the double bond does not need a number. if there is a substituent, the carbons in the double bond are numbered as 1 and 2, and the ring is numbered from carbon 2 in the direction that will give the lower number to the substituent. cyclopentene 3 -methylcyclohexene

Physical Properties of Alkenes… • Not soluble in water (hydrophobic) • M. p. /b. p. a little higher than alkanes • React because of the extra electrons between the carbons of The double bond (the pi system) • We will do reactions of alkenes & alkynes in the next class period.

Rules for naming alkynes…

What would this name be?

4 -octyne…note how planar the structure is around the atoms of the triple bond!

Where would you start numbering?

This name would be… 6 -propyl-3 -nonyne 9 7 6 8 5 4 1 3 2 Note: We started numbering by carbon “c. ”. The numbers for each Carbon are noted to help you remember to count the carbons in the Triple bond…

Draw in your composition books…

Physical Properties of Alkynes

Let’s do one more… What would this name be?

1 -Pentyne…

A few extra problems…

Learning Check Name each, using cis–trans prefixes when needed. A.

Solution A. cis-1, 2 -Dibromoethene trans-2 -Butene 1, 1 -Dichloropropene