Chapter 10 - Hydration, Dehydration, Alcohols

hydration reaction

the reaction of an alkene with water to form an alcohol

• the product contains an OH group (hydroxyl group) bonded to a carbon atom

• 2 or more atoms become bonded to original alkene and double bond becomes single bond

hydroxyl group

OH group connected to a carbon

alcohol

product of hydration reaction, contains hydroxyl group bonded directly to a hydrocarbon chain

Hydration reaction of alkenes

many alkenes produce 2 hydration reactions

the hydroxyl group can be bonded to either side of original alkene group (the double bond)

cycloalkenes can be hydrated

can react with water to form alcohol

• double bond becomes single bond, H and OH become attached to the ring

symmetrical alkenes

able to produce only 1 hydration product

• if 2 sides of the alkene are identical, we obtain the same alcohol regardless

enzyme

a protein that catalyzes a chemical reaction; holds the water molecule in place so it can only react with the alkene grp in the correct way

roles of enzymes

1. speeds up reactions

2. ensure that correct product is formed whenever 2 or more products are possible, can ensure the H and OH are placed in correct orientation

using IUPAC to name alcohol

1. name the hydrocarbon framework

2. identify the functional grp by modifying the ending of the alkane name

3. add a number to tell where the functional grp is located

step 2

to identify the alcohol grp, we replace the “-e” at the end of the alkane name with '“-ol”

2 simplest alcohols are

1. methanol

2. ethanol

step 3

• have more than one possible location for our alcohol group

• add the # before rest of name to tell us which carbon atom is bonded to functional grp

cyclic alcohol

ring of carbon atoms attached to a hydroyxl grp

naming cyclic alcohols

change the end of the name of the corresponding hydrocarbon from “-e” to “-ol”

• do not use #’s

drawing the structure of an alcohol

1. draw hydrocarbon

2. “-ol” ending tells us molecules has a hydroxyl grp, then count where the hydroxyl grp is

3. then add enough hydrogen atoms to achieve all four bonds

alcohols commonly used trivial names

(names usually contain name of alkyl group followed by alcohol)

1. methyl alcohol (methanol)

2. ethyl alcohol (ethanol)

3. isopropoyl alcohol (2 - propanol)

propertites of alcohol

• polar O-H bond allows alcohols to form hydrogen bonds

• hydrogen atom from one alcohol grp is attracted to the oxygen atom of a second alcohol grp

• boiling point of alcohol is higher than corresponding alkane

• alcohols are more soluble in water than hydrocarbons are

alcohol boiling points

BP is higher than corresponding alkane because they have stronger attractions due to their hydrogen bonds

solubility of alcohols

more soluble in water than hydrocarbons

• depends on size of carbon chain

hydroxyl grp is

hydrophillic

hydrocarbon portion is

hydrophobic

if the hydrophobic region is small

ability of hydroxyl group to form hydrogen bond dominates

• high solubility

if the hydrophobic region is large

its properties dominate and compound behaves more like an alkane

• low solubility

dehydration reaction

a reaction where an alcohol breaks down into an alkene and a molecule of water

• reverses hydration reaction

• hydrogen atom and a hydroxyl grp must be attached to neighboring carbon atoms, removing these allows the 2 carbon atoms to form an additional bond (double bond)

dehydration example (1-propanol)

1. remove OH from carbon #1

2. then have to remove hydrogen from neighboring carbon #2

dehydration reactions form more than one product

if an alcohol has more than one carbon atom next to the functional grp, it can usually yield more than one dehydration product

phenol

organic compound that contains a benzene ring bonded to a hydroxyl group (also called carbolic acid)

• hydroxyl grp can form hydrogen bonds so have high BP and dissolve well in water

• can occur in more complex molecules

phenol is a functional grp

can occur in more complex molecules

ex. thymol

thiols

an organic compound that contains a SH group bonded to an alkyl group

• oxygen atom of hydroxyl group is replaced by sulfur

• cannot form hydrogen bonds, so low BP and less soluble in water

thiols cannot form

hydrogen bonds… so they have low BP and are less soluble in water

increasing solubility of an alcohol

by adding more hydroxyl groups

• water solubility increases as we add hydrophilic groups to a carbon framework

solubility of any organic compound depends on

1. # of hydrophilic groups

2. locations of those groups

3. structure and size of carbon skeleton

solubility trends (general statements)

1. compounds with hydrogen bonding group (hydrophilic grp) dissolves better than compounds that cannot form hydrogen bonds, regardless of sizes of molecules

2. if 2 compounds have same hydrophilic grp, the molecule with the SMALLER carbon framework is more soluble

3. if 2 compounds have the same carbon framework, the molecule with MORE hydrophilic groups is the more soluble

the hydroxyl grp in alcohols are not

acidic or basic

how to recognize a true hydroxide ion in the formula of a compound

metallic element

metallic element

compounds that contain hydroxide ions also contain a metallic element, which forms a positively charged ion when dissolved in water

ex. KOH, Ca(OH)₂ , Al(OH) ₃

chiral

an object that cannot be superimposed on its mirror image

(has left and right versions that don’t match ex. hands)

superimposed

you can put one thing on top of another and they match perfectly

achiral

identical to and superimposable on its mirror image (nose)

many chemical compounds are chiral

alcohols can have 2 possible forms that are mirror images of each other

entatiomers

mirror image forms of a compound that are not superimposable

• type of stereoisomer where compound has the same atoms, connected the same way, are mirror images but cannot be stacked exactly ontop of each other

how can we recognize chiral molecules (chiral carbon molecules)

if a molecule contains a carbon atom that is bonded to FOUR DIFFERENT groups of atoms

example of not chiral molecule

• 1st and 3rd carbon their 3 grps are identical to each other

• 2nd carbon is not chiral because 2 bonded grps are identical