Macroscopic physical properties such as melting and boiling points depend on the strengths of the forces which hold microscopic particles together. In the case of molecules whose atoms are connected by covalent bonds, such intermolecular forces may be of three types. All molecules are attracted together by weak London forces. These depend on instantaneous polarization and increase in strength with the size of the molecular electron cloud. When a molecule contains atoms whose electronegativities differ significantly and the resulting bond dipoles do not cancel each other’s effects, dipole forces occur. This results in higher melting and boiling points than for nonpolar substances.
The third type of intermolecular force, the hydrogen bond, occurs when one molecule contains a hydrogen atom connected to a highly electronegative partner. The other molecule must contain an electronegative atom, like fluorine, oxygen, or nitrogen, which has a lone pair. Although each hydrogen bond is weak compared with a covalent bond, large numbers of hydrogen bonds can have very significant effects. One example of this is in the properties of water. This highly unusual liquid plays a major role in making living systems and the earth’s environment behave as they do.
Carbon normally forms four bonds, and carbon-carbon bonds are quite strong, allowing formation of long chains to which side branches and a variety of functional groups may be attached. Hence the number of molecular structures which can be adopted by organic compounds is extremely large. Functional groups containing oxygen atoms, nitrogen atoms, and multiple bonds often determine the chemical and physical properties of carbon compounds. Therefore organic chemistry may be systematized by studying related groups of compounds such as alkanes, cycloalkanes, aromatic compounds, alkenes and alkynes, alcohols, ethers, aldehydes and ketones, carboxylic acids, esters,amines, and so on. Within each of these categories chemical and physical behaviors are closely related to molecular structures. Some covalently bonded substances do not consist of individual small molecules. Instead, giant macromolecules form. Examples include most of the rocks in the crust of the earth as well as modern plastics. Properties of such substances depend on whether the macromolecules are three dimensional (like diamond), two dimensional (like graphite or sheets of mica) or one dimensional (like polyethylene). In the latter two cases the strengths of forces between adjacent macromolecules have a significant effect on the properties of the substances.

Overview of The Physical Properties of Organic Compounds
In addition to reactivity, the physical properties of an organic substance, such as melting point, boiling point and solubility, are amont its most important traits. The physical properties of an organic substance can often be predicted from its structure. In most cases, a substance's molecular weight and the functional groups are sufficient information to allow for a good estimate of the melting point, boiling point, and solubility to be estimated. Comparing molecules of similar size, the greater the strength of intermolecular force, the more equilibrium will favor the condensed phase at a given pressure and temperature.

The Physical Properties of Organic Compounds on the MCAT
Understanding how functional groups affect the physical properties of organic compounds is of primary importance to laboratory organic chemistry, and, furthermore, one of the bridges from organic chemistry to biochemistry and cell biology. The student must obtain this form of understanding to be able to grasp protein folding, for example, or the structure of biological membranes. Every MCAT makes this area a priority. You can expect both direct and indirect questions. Straightforward questions asking for a comparison of solubilities are common, for example, as are questions involving similar reasoning in a more advanced biological context.
Conceptual Vocabulary
Hydrophobicity Hydrophobicity refers to the physical property of a molecule that is repelled from a mass of water
Hydrocarbon A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon.
Hydrophilicity Hydrophilicity refers to a physical property of a molecule that can transiently bond with water through hydrogen bonding.
Miscibility Miscibility is a term in chemistry that refers to the property of liquids to mix, forming a homogeneous solution.
Lipophilicity Lipophilicity refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene.
Aliphatic compound Aliphatic compounds are organic compounds in which carbon atoms are joined together in straight or branched chains or in rings, that can be either saturated or unsaturated, but not aromatic.
Paraffin Paraffin is a common name for the group of alkane hydrocarbons.
Volatility Volatility is a measure of the speed at which a substance turns into a vapor from a solid or liquid state.
Volatile organic compound Volatile organic compounds (VOCs) are organic chemical compounds that have high enough vapour pressures under normal conditions to significantly vaporize and enter the atmosphere.
Amphiphile Amphiphile is a term describing a chemical compound possessing both hydrophilic and hydrophobic properties.
Partition coefficient A partition or distribution coefficient is the ratio of concentrations of a compound in the two phases of a mixture of two immiscible solvents at equilibrium.
Protic solvent A protic solvent is a solvent that carries a hydrogen bond between an oxygen as in a hydroxyl group or a nitrogen as in an amine group.
Liquid-liquid extraction Liquid-liquid or solvent extraction, also known as partitioning, is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent.
Hygroscopy Hygroscopy is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption.
Multiphasic liquid A multiphasic liquid is a mixture consisting of more than two immiscible liquid phases.
Relative volatility Relative volatility is a measure of the vapor pressure differences of the components in a liquid mixture of chemicals.
Advanced terms that may appear in context in MCAT passages
Bolaamphiphile Bolaamphiphiles are amphiphilic molecules that have hydrophilic groups at both ends of a sufficiently long hydrophobic hydrocarbon chain.
Lipophobicity Lipophobicity is a term which literally means fat rejection and describes compounds which are not soluble in lipids or other non-polar solvents.
Flory-Huggins solution theory Flory-Huggins solution theory is a mathematical model of the thermodynamics of polymer solutions which takes account of the great dissimilarity in molecular sizes in adapting the usual expression for the entropy of mixing.
Lyotropic A material is called lyotropic if it forms liquid crystal phases because of the addition of a solvent.

* Boiling Points

The boiling point of each alkene is very similar to that of the alkane with the same number of carbon atoms. Ethene, propene and the various butenes are gases at room temperature. All the rest that you are likely to come across are liquids.

In each case, the alkene has a boiling point which is a small number of degrees lower than the corresponding alkane. The only attractions involved are Van der Waals dispersion forces, and these depend on the shape of the molecule and the number of electrons it contains. Each alkene has 2 fewer electrons than the alkane with the same number of carbons.
The carbon atom is always
Attached to the hydrogen atoms

Structural formula, Condense structural formula, and Line-angle formula

The pattern of the boiling point of alkanes, alkenes and alkynes are from the lowest degree of the hydrocarbons compounds such as negative to positive, lowest to highest or from the coldest to hottest degree.

Artist: Fray
Album: How To Save A Life
Song: How To Save A Life
Lyrics:

Step one you say we need to talk
He walks you say sit down it's just a talk
He smiles politely back at you
You stare politely right on through
Some sort of window to your right
As he goes left and you stay right
Between the lines of fear and blame
And you begin to wonder why you came

Where did I go wrong, I lost a friend
Somewhere along in the bitterness
And I would have stayed up with you all night
Had I known how to save a life

Let him know that you know best
Cause after all you do know best
Try to slip past his defense
Without granting innocence
Lay down a list of what is wrong
The things you've told him all along
And pray to God he hears you
And pray to God he hears you

Where did I go wrong, I lost a friend
Somewhere along in the bitterness
And I would have stayed up with you all night
Had I known how to save a life

As he begins to raise his voice
You lower yours and grant him one last choice
Drive until you lose the road
Or break with the ones you've followed
He will do one of two things
He will admit to everything
Or he'll say he's just not the same
And you'll begin to wonder why you came

Where did I go wrong, I lost a friend
Somewhere along in the bitterness
And I would have stayed up with you all night
Had I known how to save a life

Artist:Timbaland feat. One Republic
Album: Shock Value
Song: Apologize
Lyrics:
I'm holding on your rope,
Got me ten feet off the ground
I'm hearin what you say but I just can't make a sound
You tell me that you need me
Then you go and cut me down, but wait
You tell me that you're sorry
Didn't think I'd turn around, and say...

It's too late to apologize, it's too late
I said it's too late to apologize, it's too late

I'd take another chance, take a fall
Take a shot for you
And I need you like a heart needs a beat
But it's nothin new - yeah yeah
I loved you with a fire red-
Now it's turning blue, and you say...
"Sorry" like the angel heaven let me think was you
But I'm afraid...

It's too late to apologize, it's too late
I said it's too late to apologize, it's too late

It's too late to apologize, it's too late
I said it's too late to apologize, it's too late
It's too late to apologize, yeah
I said it's too late to apologize, yeah-
I'm holdin on your rope, got me ten feet off the ground...