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In the molecule below, how many atoms could make hydrogen bonds with water?

A structure of a molecule. It has a H2CCHCCHCH2CH2CCH2CCOOH backbone with an oxygen atom double-bonded to the seventh (from left to right) carbon. There are double bonds between the first and the second carbon atoms and between the third and the fourth carbon atoms. A CH2OPO group is attached to the third carbon. In this group, there are two OH groups attached to the phosphorus and the bond between the phosphorus and the second (from left to right) oxygen of the CH2OPO group is a double one. A CHCH2SH group is double-bonded to the ninth carbon.

5
7
10
12

1 answer

To determine how many atoms in the given molecule could potentially make hydrogen bonds with water, we need to identify the functional groups that can participate in hydrogen bonding.

Key points to consider for hydrogen bonding:

  • Hydrogen bonds typically involve hydrogen atoms bonded to electronegative atoms (like oxygen, nitrogen, or fluorine) and lone pairs on these or other electronegative atoms.

Now, let's break down the molecule based on the description provided:

  1. Carboxylic Group (COOH):

    • The OH in the carboxylic acid group can participate in hydrogen bonding. Thus, contributes 1 hydrogen (H) and 1 oxygen (O) for potential hydrogen bonding.

  2. CH2OPO group with two OH groups:

    • Each OH group can also form hydrogen bonds.
    • If there are two OH groups from this phosphoric acid derivative, this contributes 2 hydrogens (H) and 2 oxygens (O).

  3. SH group (Thiol):

    • The -SH group can participate in hydrogen bonding as well, but it is generally a weaker hydrogen bond compared to -OH. Still, this contributes 1 hydrogen (H) and 1 sulfur (S), although sulfur is less electronegative than oxygen, it's still worth considering in some contexts.

Summarizing the contributions:

  • From the COOH: 1 H, 1 O
  • From the two OHs in CH2OPO: 2 Hs, 2 Os
  • From the SH: 1 H, (though we note there isn’t a strong hydrogen bond with sulfur compared to oxygen)

Altogether:

  • Hydrogens: 4 (1 from COOH + 2 from 2 OHs + 1 from SH)
  • Oxygens: 3 (1 from COOH + 2 from 2 OHs)

Counting only the hydrogen bond potential:

  • 4 Hydrogens can participate in hydrogen bonding (from both the COOH and OH groups; while the hydrogen from SH can also bond, it's less favorable).
  • 3 Oxygens can potentially bond as they are bonded to hydrogen or can donate lone pairs.

Therefore, counting actual atoms that participate in hydrogen bonding:

  • The strongest hydrogen bond donors are typically considered the oxygen and hydrogen atoms bound to them.
  • Hence, we have 3 oxygen atoms and 4 hydrogen atoms participating in bonds.

Final computation of bonding atoms:

  • 3 Oxygen (O from carboxylic group & OHs)
  • Up to 4 Hydrogens (H from carboxylic group & OHs)

In total, a reasonable assumption here would be 6 atoms that can be considered to participate in hydrogen bonding with water.

However, none of the provided options (5, 7, 10, 12) represent this total count directly. Nonetheless, if we have to select from the given options carefully or estimate based on the strongest participants, other interpretations might suggest considering how many potential hydrogen bond interactions could occur rather than strictly the atoms involved.

Thus, if we explore further to select the next reasonable count or a common exam context that pulls from practical assumptions on hydrogen bond forming abilities, considering possible targets alongside structural interpretation might lead one to suggest '5' as closest to the stronger functional groups present.

Final conclusion: 5 atoms could potentially be considered for hydrogen bonding with water.