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 * ALKANES**


 * __PROPERTIES OF ALKANES__**


 * HOMOLOGOUS SERIES** is one in which all members have the same general formula. The neighboring members of the series differ by - CH2 -, and they show similar chemical properties and a gradation in their physical properties. The first 4 members of the homologous series of the alkanes are methane, ethane, propane, and butane. All four are gases under STP, although their boiling points increase as the number of carbon atoms increases. All four gases have similar chemical properties. They are good fuels, because they burn in a plentiful supply of oxygen to produce carbon dioxide and water. They also react with halogens in ultraviolet light, but otherwise they are quite unreactive.


 * ISOMERS** are formed when 2 or more compounds have the same molecular formula but a different structural formula. The trend of their boiling points increases as the parent chain becomes longer.

__** REACTIONS OF ALKANES **__

Alkanes are unreactive as a family because of the strong C - C bonds and C - H bonds as well as them being non-polar compounds. At room temperature, alkanes do not react with acids, bases, or strong oxidizing agents.

However, alkanes do undergo **COMBUSTION** in air (making them good fuels):

EXAMPLE: 2C2H6 (g) + 7O2 (g) --> 4CO2 (g) + 6H2O (l)

**COMPLETE COMBUSTION** is a rapid chemical combination of a substance with oxygen, involving the production of heat and light. Complete combustion produces carbon dioxide and water.

**INCOMPLETE COMBUSTION** is wherein alkanes burn with insufficient oxygen for a complete combustion. The products of incomplete combustion may have a combination of carbon monoxide, carbon, and water in addition to carbon dioxide.

EXAMPLE OF COMPLETE COMBUSTION: 2C8H18 (l) + 25O2 (g) --> 16CO2 + 18H2O (l) EXAMPLE OF INCOMPLETE COMBUSTION: C8H18 (l) + 9O2 (g) --> C (s) + 5CO (g) + 2CO2 + 9H2O (l)

Apart from combustion, the other type of reaction that alkanes readily undergo is with the halogens. In the dark, there is no reaction, but in ultraviolet light, a rapid substitution reaction takes place. In this substitution reaction, one atom of a molecule is removed and replaced or substituted by another atom or a group of atoms. This mechanism of substitution reaction involves free radicals. An example of this reaction is given below:

CH4 (g) + Cl2 (g) --> CH3Cl (g) + HCl (g)

This reaction takes places in a series of separate steps. The **REACTION MECHANISM** of an organic reaction describes and explains these steps. Overall, this particular reaction mechanism is known as **FREE RADICAL SUBSTITUTION**. The first step, known as the **INITIATION STEP**, involves the formation of free radicals. It is for this reason that the reaction occurs only in the presence of ultraviolet light, because this provides the energy to break the chlorine-to-chlorine bond **HOMOLYTICALLY**.

This produces chlorine atoms in a form known as **FREE RADICALS**. Free radicals contain an unpaired electron in one of their orbitals, and are a highly energetic and reactive species. When a chlorine free radical collides with a methane molecule, it reacts to form hydrogen chloride and another free radical. This methyl radical can react with a molecule of chlorine, and the product, chloromehtane, is formed. At the same time, another chlorine free radical has been generated. These two steps are known as **PROPAGATION STEPS** because in each step radicals react to generate (propagate) new radicals. Once the ultraviolet light has initiated the formation of free radicals, then one radical can effectively go on to produce many molecules of products. However, there will also be **TERMINATION STEPS**. The radicals may collide with the walls of the vessel, or escape completely, or they may react with another free radical to produce a non-radical product. In fact, a trace of ethane can be found in the products, which provides good evidence for the free radical mechanism.


 * STEPS OF THE MECHANISM FOR THE RADICAL SUBSTITUTION REACTION BETWEEN METHANE AND CHLORINE IN ULTRAVIOLET LIGHT **

1) INITIATION

Cl – Cl (g) à 2Cl (g) (reaction happen in UV light)

2) PROPAGATION

Cl (g) + CH4 (g) à CH3 (g) + HCl (g)

CH3 (g) + Cl2 (g) à CH3Cl (g) + Cl (g)

3) POSSIBLE TERMINATION STEPS

Cl (g) + Cl (g) à Cl2 (g)

Cl (g) + CH3 (g) à CH3Cl (g)

CH3 (g) + CH3 (g) à C2H6 (g)

4) OVERALL REACTION

Cl2 (g) + CH4 à CH3Cl (g) + HCl (g)

Reactions Mechanism of Halogens and Alkanes

[] media type="youtube" key="VIHtLIb-oZo?fs=1" height="385" width="480"

Sources:

Chemistry: Course Companion by Geoffrey Neuss (pp. 192 - 193)


 * ALKENES**


 * __PROPERTIES OF ALKENES__**

Alkenes contain a carbon-to-carbon double bond. They form a homologous series with the general formula C(n)H(2n). The simplest alkene is ethene, C2H4. Alkenes are named by taking the longest chain and then specifying where the double bond begins.

The physical properties of alkenes are very similar to those of alkanes, as they are either non-polar or have very low polarity. Like alkanes, they have low boiling points, which increase as the molar mass increases, and they are insoluble in polar solvents such as water.

Like all hydrocarbons, alkenes burn in excess oxygen to give carbon dioxide and water as the products of complete combustion.

C(n)H(2n) + (n + n / 2) O2 (g) = nCO2 (g) + nH2O (l)

In air where the amount of oxygen is limited, they burn with a more yellow and sooty flame than alkanes, as more incomplete combustion occurs. Apart from combustion, because of the presence of the double bond in alkenes their other chemical properties are very different from those of alkanes.

Compounds of carbon and hydrogen that contain one double covalent bond between carbon atoms (carbon=carbon) or a triple covalent bond between carbon atoms are called **UNSATURATED HYDROCARBONS** (alkenes and alkynes). In these molecules, since all the bonds of carbon are not fully utilised by hydrogen atoms, more of these can be attached to them. Thus, they undergo addition reactions (add on hydrogen) as they have two or more hydrogen atoms less than the **SATURATED HYDROCARBONS** (alkanes).

__**REACTIONS OF ALKENES**__


 * HYDROGENATION** of alkenes produces the corresponding alkanes. The reaction is carried out under pressure at a temperature of 200 °C in the presence of a metallic catalyst. Common industrial catalysts are based on platinum, nickel or palladium. The simplest example of this reaction is the catalytic hydrogenation of ethylene to yield ethane:

CH 2 =CH 2 + H 2 → CH 3 -CH 3


 * HALOGENATION**

In electrophilic halogenation the addition of elemental bromine or chlorine to alkenes yields vicinal dibromo- and dichloroalkanes (1,2-dihalides or ethylene dihalides), respectively. The decoloration of a solution of bromine in water with dichloromethylene as catalyst is an analytical test for the presence of alkenes: CH2=CH2 + Br2 → BrCH2-CH2Br It is also used as a quantitive test of unsaturation, expressed as the bromine number of a single compound or mixture. The reaction works because the high electron density at the double bond causes a temporary shift of electrons in the Br-Br bond causing a temporary induced dipole. This makes the Br closest to the double bond slightly positive and therefore an electrophile.

Alkenes 101 Videoes: Bonding, Shapes and drawing: media type="youtube" key="m1FUvIHplBE?fs=1" height="385" width="480" E-Z isomerism:

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Electrophilic Addition Reaction:

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Markonikov's Rule:

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Polymerisation:

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__** ORGANIC DERIVATIVES **__

**ALDEHYDES** is a carbonyl compound like ketone. Both aldehydes and ketones are organic compounds in which the carbonyl carbon is connected to C or H atoms on either side. An aldehyde has one or both vacancies of the carbonyl carbon satisfied by a H atom, while a ketone has both its vacancies satisfied by carbon.

Aldehydes are named by replacing the -e ending of an alkane with -al for an aldehyde. Since an aldehyde is always at the carbon that is numbered one, a number designation is not needed. For example, the aldehyde of pentane would simply be pentanal. The ( -CH=O ) group of aldehydes is known as a formyl group. When a formyl group is attached to a ring, the ring name is followed by the suffix "carbaldehyde". For example, a hexane ring with a formyl group is named cyclohexane carbaldehyde.

Aldehyde's polarity is characterized by the high dipole moments of their carbonyl group, which makes them rather polar molecules. It is more polar than alkenes and ethers. Because they lack hydrogen, they cannot participate in hydrogen bonding like alcohols, thus making their relative boiling points higher than alkenes and ethers, yet lower than alcohols. Also, aldehydes have Van der Waals dispersion forces making them have a high boiling point as well.

Aldehydes are soluble in water. However, as the number of carbon chain length increases (parent chain), the solubility falls. The reason for the solubility is that although aldehydes cannot undergo hydrogen bonding with themselves, they can hydrogen bond with water molecules. One of the slightly positive hydrogen atoms in a water molecule can be sufficiently attracted to one of the lone pairs on the oxygen atom of an aldehyde for a hydrogen bond to be formed. There will also, of course, be dispersion forces and dipole-dipole attractions between the aldehyde and the water molecules. Forming these attractions releases energy which helps to supply the energy needed to separate the water molecules and aldehyde from each other before it can mix together. As chain lengths increase, the hydrocarbon "tails" of the molecules (all the hydrocarbon bits apart from the carbonyl group) start to get in the way. By forcing themselves between water molecules, they break the relatively strong hydrogen bonds between water molecules without replacing them by anything as good. This makes the process energetically less profitable, and so solubility decreases.



Ketone:

Ketones have a pair of alkyl or aromatic groups attached to a carbonyl function.

The structure of Ketones can be shown as RCOR

Features a carbonyl group (C=O) bonded to two other carbon atoms.

Belongs to the functional group of RCOR or known as a carbonyl where :

There are three types of ketones which are specifically : (Diketones, Unsaturated Ketones, Cyclic Ketones)

Diketones

- A diketone is a molecule that consists of two ketone groups and one of the known diketones is diacetyl.

Unsaturated Ketones

-These are ketones that contain alkene and alkyne units

Cyclic Ketones

-Composes most of the Ketones

-Given by its name, the structure is cyclic

Physical Properties:

Boiling Point: The boiling point increases as the ketone molecule gets bigger, since size is governed by the strength of intermolecular forces

Solubility in Water

Ketones are freely soluble in water but its solubility rate decreases as the chain length increases

Volatility:

Relatively High

**ALCOHOLS** are the family of compounds that contain one or more hydroxyl (-OH) groups. Alcohols are represented by the general formula R-OH. Alcohols are important in organic chemistry because they can be converted to and from many other types of compounds. Reactions with alcohols fall into two different categories. Reactions can cleave the R-O bond or they can cleave the O-H bond. Examples are ethanol (ethyl alcohol, or grain alcohol), which is found in alcoholic beverages, CH3CH2OH.

Follow these rules to name alcohols the IUPAC way:
 * 1) find the longest carbon chain containing at least one OH group, this is the parent
 * 2) if there are multiple OH groups, look for the chain with the most of them, and the way to count as many carbons in that chain
 * 3) name as an alcohol, alkane diol, triol, etc.
 * 4) number the OH groups, giving each group the lowest number possible when different numbering possibilities exist
 * 5) treat all other groups as lower priority substituents (alcohol / hydroxy groups are the highest priority group for naming)

In an O-H bond, the O steals the H's electron due to its electronegativity, and O can carry a negative charge (R-O-). This leads to deprotonation in which the nucleus of the H, a proton, leaves completely. This makes the -OH group (and alcohols) Bronsted acids. Alcohols are weak acids, even weaker than water. Ethanol has a pKa of 15.9 compared to water's pKa of 15.7. The larger the alcohol molecule, the weaker an acid it is.

On the other hand, alcohols are also weakly basic. This may seem to be contradictory--how can a substance be both an acid and a base? However, substances exist that can be an acid or a base depending on the circumstances. Such a compound is said to be amphoteric or amphiprotic. As a Bronsted base, the oxygen atom in the -OH group can accept a proton (hydrogen ion.) This results in a positively-charged species known as an oxonium ion. Oxonium ions have the general formula ROH2+, where R is any alkyl group.

Oxidation in organic chemistry always involves either the addition of oxygen atoms (or other highly electronegative elements like sulfur or nitrogen) or the removal of hydrogen atoms. Whenever a molecule is oxidized, another molecule must be reduced. Therefore, these reactions require a compound that can be reduced. These compounds are usually inorganic. They are referred to as oxidizing reagents. With regards to alcohol, oxidizing reagents can be strong or weak. Weak reagants are able to oxidize a primary alcohol group into a aldehyde group and a secondary alcohol into a ketone. Thus, the R-OH (alcohol) functional group becomes R=O (carbonyl) after a hydrogen atom is removed. Strong reagents will further oxidize the aldehyde into a carboxylic acid (COOH). Tertiary alcohols cannot be oxidized. An example of a strong oxidizing reagent is chromic acid (H2CrO4). An example of a weak oxidizing reagent is pyridinium chlorochromate (PCC) (C5H6NCrO3Cl).


 * COMBUSTION OF ALCOHOLS **

All alcohols burn readily in a plentiful supply of oxygen to form carbon dioxide and water. Alcohols are already partially oxidized, as they contain an oxygen atom. This can be verified by comparing the standard enthalpies of combustion of ethanol and octane:

Example: C2H5 + 3O2 --> 2CO2 + 3H2O


 * OXIDATION OF PRIMARY, SECONDARY, AND TERTIARY ALCOHOLS **

Ethanol is an example of a primary alcohol. **Primary alcohols** contain two hydrogen atoms and one alkyl group bonded to the carbon atom that contains the alcohol group. Secondary alcohols contain one hydrogen atom and two alkyl groups bonded directly to the carbon containing the alcohol group. Tertiary alcohols contain three alkyl groups and no hydrogen atoms bonded to the carbon atom containing the alcohol group.

Primary alcohols can be oxidised to either aldehydes or carboxylic acids depending on the reaction conditions. In the case of the formation of carboxylic acids, the alcohol is first oxidised to an aldehyde which is then oxidised further to the acid.

You get an aldehyde if you use an excess of the alcohol, and distil off the aldehyde as soon as it forms. The excess of the alcohol means that there isn't enough oxidising agent present to carry out the second stage. Removing the aldehyde as soon as it is formed means that it doesn't hang around waiting to be oxidised anyway! If you used ethanol as a typical primary alcohol, you would produce the aldehyde ethanal, CH3CHO. The full equation for this reaction is fairly complicated, and you need to understand about electron-half-equations in order to work it out.



In organic chemistry, simplified versions are often used which concentrate on what is happening to the organic substances. To do that, oxygen from an oxidising agent is represented as [O]. That would produce the much simpler equation:

**Secondary alcohols** are oxidised to ketones - and that's it. For example, if you heat the secondary alcohol propan-2-ol with sodium or potassium dichromate(VI) solution acidified with dilute sulphuric acid, you get propanone formed. If you look at what is happening with primary and secondary alcohols, you will see that the oxidising agent is removing the hydrogen from the -OH group, and a hydrogen from the carbon atom attached to the -OH. Tertiary alcohols don't have a hydrogen atom attached to that carbon. You need to be able to remove those two particular hydrogen atoms in order to set up the carbon-oxygen double bond.
 * Tertiary alcohols** aren't oxidised by acidified sodium or potassium dichromate(VI) solution. There is no reaction whatsoever.

= = =Alkyl Halides=

An **alkyl halide** is another name for a halogen-substituted alkane. The carbon atom, which is bonded to the halogen atom, has sp 3 hybridized bonding orbitals and exhibits a tetrahedral shape. Due to electronegativity differences between the carbon and halogen atoms, the σ covalent bond between these atoms is polarized, with the carbon atom becoming slightly positive and the halogen atom partially negative. Halogen atoms increase in size and decrease in electronegativity going down the family in the periodic table. Therefore, the bond length between carbon and halogen becomes longer and less polar as the halogen atom changes from fluorine to iodine.

**Nomenclature** Alkyl halides are named using the IUPAC rules for alkanes. Naming the alkyl group attached to the halogen and adding the inorganic halide name for the halogen atom creates common names.

Functional group suffix = //-halide// Functional group prefix = //halo-// Primary, secondary or tertiary ? In a similar fashion to alcohols, alkyl halides are described as primary (1 o ), secondary (2 o ) or tertiary (3 o ) depending on how many alkyl substiutents are attached to the C-X unit.



**Physical properties**

Alkyl halides have little solubility in water but good solubility with nonpolar solvents, such as hexane. Many of the low molecular weight alkyl halides are used as solvents in reactions that involve nonpolar reactants, such as bromine. The boiling points of different alkyl halides containing the same halogen increase with increasing chain length. For a given chain length, the boiling point increases as the halogen is changed from fluorine to iodine. For isomers of the same compound, the compound with the more highly-branched alkyl group normally has the lowest boiling point. Table [|1] summarizes data for some representative alkyl halides.



**Structure:**
 * The alkyl halide functional group consists of an sp 3 hybridised C atom bonded to a halogen, X, via a s bond.
 * The carbon halogen bonds are typically quite polar due to the electronegativity and polarisability of the halogen.

**Reactivity:** Read more: [|http://www.cliffsnotes.com/study_guide/Introduction-to-Alkyl-Halides.topicArticleId-23297,articleId-23251.html#ixzz17JHCgy7r]
 * The halogens (Cl, Br and I) are good leaving groups.
 * The polarity makes the C atom electrophilic and prone to attack by nucleophiles via [|SN1] or [|SN2] reactions.
 * Bases can remove b -hydrogens and cause 1,2-elimination to form alkenes via E1 or E2 reactions.
 * Insertion of a metal (esp. Mg) creates an organometalic species.

=** Carboxylic Acid **=

Carboxylic acids are compounds which contain a -COOH group. For the purposes of this page we shall just look at compounds where the -COOH group is attached either to a hydrogen atom or to an alkyl group.

**Physical properties of carboxylic acids** The physical properties (for example, boiling point and solubility) of the carboxylic acids are governed by their ability to form hydrogen bonds. **Boiling points** Before we look at carboxylic acids, a reminder about alcohols: The boiling points of alcohols are higher than those of alkanes of similar size because the alcohols can form hydrogen bonds with each other as well as van der Waals dispersion forces and dipole-dipole interactions. The boiling points of carboxylic acids of similar size are higher still. These are chosen for comparison because they have identical relative molecular masses and almost the same number of electrons (which affects van der Waals dispersion forces). The higher boiling points of the carboxylic acids are still caused by hydrogen bonding, but operating in a different way. In a pure carboxylic acid, hydrogen bonding can occur between two molecules of acid to produce a **//dimer//**.

This immediately doubles the size of the molecule and so increases the van der Waals dispersion forces between one of these dimers and its neighbours - resulting in a high boiling point.

**Solubility in water** In the presence of water, the carboxylic acids don't dimerise. Instead, hydrogen bonds are formed between water molecules and individual molecules of acid. The carboxylic acids with up to four carbon atoms will mix with water in any proportion. When you mix the two together, the energy released when the new hydrogen bonds form is much the same as is needed to break the hydrogen bonds in the pure liquids. The solubility of the bigger acids decreases very rapidly with size. This is because the longer hydrocarbon "tails" of the molecules get between water molecules and break hydrogen bonds. In this case, these broken hydrogen bonds are only replaced by much weaker van der Waals dispersion forces.


 * ORGANIC CHEMISTRY HL (Steven, Marvin, James)**

**AMINES**

They are organic derivatives of ammonia, meaning that one, two, or three hydrocarbon groups have replaced the hydrogens in ammonia. Some examples are methylamine ( CH3 - NH2), dimethylamine ( CH3 - NH2 - CH3), etc. The NH bond is not as polar as the OH bond in alcohols, so amines boil at lower temperatures than alcohols of comparable molecular masses. Amines which have low molecular masses are soluble in water because of hydrogen bonding. This is also why trimethylamine has a lower boiling point than dimethylamine (even though its bigger), because there is no NH bond to cause significant hydrogen bonding.

Amines can be named in two ways. The first way is adding the prefix word AMINO-, with the location of the -NH2 group being indicated: for example, 2-aminopentane and 1,6-diaminohexane. Another way is to by calling them using the longest alkane chain and adding the suffix -amine: for example, 2-ethylamine.

Amines are organic compounds that contain a nitrogen atom with a lone pair for example:
 * **Primary amine** || **Secondary amine** || **Tertiary amine** ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/7/7f/Methylamine-2D.png width="109" height="81"]] || [[image:http://upload.wikimedia.org/wikipedia/commons/f/f9/Dimethylamine.png width="565" height="268" align="center"]] || [[image:http://www.bmrb.wisc.edu/metabolomics/standards/trimethylamine/lit/3844.png width="189" height="215"]] ||

The amine's functional group would be the group -NH2. Since there is an abundance of amines, the easiest way to think of amines by making use of its near relative which is ammonia as they nearly have the same structure

Amines can be classified into three groups primarily: (Primary, Secondary & Tertiary)

Primary Amines: In primary amines, only one hydrogen atoms in the ammonia molecule would be replaced. This means that the formula of the primary amine would be RNH2 where R is an alkyl group

Examples: methylamine

Secondary Amines:

For secondary amines, two of the hydrogen atoms in ammonia would be replaced by hydrocarbon groups. Also at this level, there may be encounters of same alkyl groups

Example: dimethylamine

Tertiary Amines:

Lastly, in this level all hydrogen atoms in an ammonia molecule would be replaced by hydrocarbon groups. Just like its secondary brother, there may be chances where the same alkyl group can be found.

Example: trimethylamine

Physical Properties:

Boiling Point: There are no actual boiling points of amines as there is an abundant presence of amines. However, the boiling point can be accounted as it has a higher boiling point than phosphines while it has a lower boiling point than alcohols.

Primary Amines: It has the ability to form hydrogen bonds, thus it has the capability of having a high boiling point.

Boiling points also increase as the chain length increases

Secondary Amines:

Boiling points of secondary amines are a little lower than those of primary amines, but it too has the capabilities of forming hydrogen bonds.

Tertiary Amines:

The boiling point of a tertiary amine would be lower than other of the classifications as it does not have the ability to form hydrogen bonds, since all hydrogen bonds have been replaced by hydrocarbons.

Solubility:

Small amines of all types are very soluble in water. Aside from this the Nitrogen atom of all types of amines in the molecule has the capability of forming a hydrogen bond. Solubility only falls as the hydrocarbon chain gets longer

Volatility and Acidity:

Amines have a relatively high volatility

Amines are bases, hence their pH level would be higher than 7. Compared to to alkali metal hydroxides, amines would have a lower scale as they are weaker.
 * Additional facts of its basicity

Its basicity depends on the following: 1)Electronic properties of the substituents 2)Steric hindrance offered by the groups on nitrogen 3)Degree of salvation of the protonated amine

Source: []

**AMIDES**

These are derived from carboxylic acids. Instead of the carbon chain ending in -COOH, the OH part is replaced with -NH2, thus amides contain the -CONH2 group.

EXAMPLES:



PHYSICAL PROPERTIES

1) The melting points of amides are high for the size of the molecules because they can form hydrogen bonds. The hydrogen atoms in the -NH2 group are sufficiently positive to form a hydrogen bond with a lone pair on the oxygen atom of another molecule.