1.4 Hydrogen bonds are very common in biological macromolecules

withdraws, negative, positive

Covalent bonds are often polarized, which means that one of the atoms participating in the bond ________ electrons towards it. This leads to the generation of an electric dipole, with the electron-withdrawing atom having a partial ___ charge and the other atom in the bond having a partial __ charge

attract

The more positive the value of the electronegativity, the greater the tendency of the atom to ____ electrons. The most common electronegative atoms in biological systems are oxygen (3.4 on the Pauling electronegativity scale) and nitrogen (3.0), while carbon (2.6) and hydrogen (2.1) are relatively electropositive (that is, they have a lesser tendency to attract electrons)

polarized

If two atoms that are covalently bonded have different electronegativities, then the bond will be _____, with the more electronegative atom being the one with the partial negative charge.

polarization

The extent of ____ is related to the difference in the electronegativities of the atoms

electric dipole

An _____ ___ is a system of charges that have a separation of positive and negative charges,

Polarization

______ is the distortion of a negatively charged ion's electron cloud by a positively charged ion. The molecule has a dipole moment because of polarisation.

polar

A ____ molecule is one that contains positive and negative poles

polar

Molecules or groups of atoms containing polarized covalent bonds are called _____ molecules/groups

nonpolar

Conversely, molecules or groups that do not contain strongly polarized covalent bonds are called ___ molecules or groups.

favorably

Two dipoles interact ____ when they are aligned so that the positive pole of one points towards the negative pole of the other

hydrogen

a particularly important example of dipoles interacting favorably with each other is the formation of ____ bond

positive

When a hydrogen is covalently bonded to a more electronegative atom (for example, nitrogen or oxygen), then the bond is polarized and the hydrogen has a partial _____ charge.

hydrogen bond

If the hydrogen is close to an electronegative atom (for example, oxygen or nitrogen) covalently bonded to a less electronegative one (for example, carbon), then a favorable dipole–dipole interaction can result, which is called the ________ ______.

donor, acceptor

The atom bearing the hydrogen is called the hydrogen-bond ______ and the atom that interacts closely with the hydrogen is called the hydrogen-bond _____

polar

Hydrogen bonds are interactions between __ groups in which a hydrogen atom with a partial positive charge is located close to an atom with a partial negative charge, called the acceptor. The partial positive charge on the hydrogen atom is a consequence of a polarized covalent bond with a more electronegative atom, called the donor

distance, close, linear

The dipole–dipole interaction falls off quickly with _____ (Figure 1.12), so that hydrogen bonds are energetically favorable only when the atoms are very _____ to one another and are also oriented appropriately (the interaction energy falls off if the angle between the dipoles is too far from ____).

water

Just as for ion pairs, the presence of ______ weakens the strength of hydrogen bonds.

hydrogen

In addition to electrostatic shielding, which weakens the Coulomb interaction energy between charges, an additional attenuation arises because water is a very polar molecule that forms strong ___ bonds with itself and with other polar molecules.

strength

Water can form strong hydrogen bond with polar groups in biological molecules. Formation of hydrogen bonds between polar groups of these molecules requires the release of water, which reduced the effective ____ of the hydrogen bond

net

In this case a hydrogen bond is formed between an N–H group and a nitrogen in an aromatic ring system. In such cases the hydrogen bond can still be thought of as a dipole–dipole interaction because the distribution of partial charges in the ring generates a __ dipole moment that arises from adding up component dipole moments, as shown in Figure 1.14B.

neutral, charged

A "__ polar" molecule has a uneven distribution of charge, creating partially positive and negative regions within the molecule, but overall has no net charge, while a "___ polar" molecule also has an uneven charge distribution, but possesses a total positive or negative charge due to the presence of ions or charged functional groups

stronger, stronger

Hydrogen bonds between polar groups that are net neutral are typically 5–20 times ____ than van der Waals attractions, after accounting for attenuation by water (see Figure 1.12). Polar groups bearing full charges can also form hydrogen bonds, and these are _____ than those between groups that do not have an overall charge